The House is pushing ahead with its public impeachment hearings this week. And with at least nine witnesses set to testify, it’s going to be an intense one.

Three people will appear on Wednesday, including the most anticipated witness of these hearings so far, US ambassador to the European Union Gordon Sondland. In the text of his opening statement, Sondland writes he “came to believe” the White House would hold up military aid until Ukraine agreed to announce an investigation into Hunter Biden’s time on the board of the energy company, Burisma. Sondland writes he was concerned about a “quid pro quo.”

Sondland also testified that his efforts were directed by Rudy Giuliani, the president’s personal lawyer. And, Giuliani, Sondland said, acted on the “orders” of President Trump.

That echoes what he said in a late amendment to his closed-door his testimony — he updated his October testimony to admit that he told a top Ukrainian official that military aid to Ukraine was likely conditioned a public announcement into those investigations.

Two other officials will follow Sondland on Wednesday: Laura Cooper, a deputy assistant secretary at the Defense Department, and David Hale, undersecretary of state for political affairs at the State Department.

House Democrats have been looking into whether President Donald Trump purposefully withheld US military aid to Ukraine and a presidential meeting in order to pressure Ukrainian President Volodymyr Zelensky to open investigations into Trump’s political rivals — namely, Joe Biden.

The cast of characters has grown immensely throughout their inquiry, and now includes three ambassadors, multiple White House, State Department, and Pentagon staffers, Cabinet members, Ukrainian officials — and even the US and Ukrainian presidents.

But wait, who are all these people? As last week’s hearing showed, tons of names are bandied about as lawmakers try to learn the full story of Trump’s Ukraine policy — or try to protect him from being impeached.

So we’ve put together a list of the main players you need to know in this drama, including all the US officials testifying in the coming days and other figures who are likely to be mentioned or whose testimony has — or may still — shape the narrative around impeachment.

We didn’t include Trump because, you know, we figured you had that covered.

The witnesses testifying, or who have testified, this week

Gordon Sondland

Sondland is a wealthy real-estate developer who donated to Trump’s inauguration; his reward was the plum posting of US ambassador to the European Union. Sondland was deeply involved in the shadow campaign to pressure Ukraine to investigate Trump’s political rivals.

In a now infamous text exchange from September 2019, William Taylor, the top diplomat in Ukraine, texted Sondland to ask whether US military aid to Ukraine and a White House meeting between Trump and Zelensky were being conditioned on Ukraine launching investigations into Trump’s political rivals. Sondland cryptically replied, “Call me.”

About a week later, Taylor again texted Sondland, writing, “As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign.” Sondland responded by denying that this was the case — and urging Taylor not to text about the matter anymore.

Sondland initially testified that there was no quid pro quo involving withheld military aid to Ukraine, but he later revised his testimony to say that even though he hadn’t recalled it earlier, yes, Ukrainian aid was in fact made contingent on investigations.

He will testify in an open hearing on Wednesday morning at 9:30 am Eastern.

Laura Cooper

She’s the Defense Department’s deputy assistant secretary for Russia, Ukraine, and Eurasia and thus the top Pentagon official working on Ukraine. In closed-door testimony last month, she told investigators that the White House had directed the freeze on aid to Ukraine and that Kyiv was concerned by the stalled support.

She will testify in an open hearing on Wednesday afternoon at about 2:30 pm Eastern.

David Hale

Hale is the State Department’s undersecretary of state for political affairs. He’s the highest-ranking career diplomat in the foreign service. Hale reportedly told the impeachment inquiry behind closed doors that Secretary of State Mike Pompeo and other senior officials didn’t want to protect ousted US ambassador to the Ukraine Yovanovitch because it could hurt the chances of military aid flowing to Ukraine.

He will testify in a public hearing alongside Cooper on Wednesday at 2:30 pm Eastern.

Lt. Col. Alexander Vindman

Vindman is an Army officer who currently serves as the director for European affairs on the National Security Council, working first under Fiona Hill and then under Tim Morrison as their point person on defense-related issues involving Russia and Ukraine.

Vindman listened in to the July 25 call and offered damning testimony to House lawmakers last month in which he described the president making a clear quid pro quo “demand” of Zelensky: a White House meeting in return for investigations into the Bidens.

Vindman also testified that the White House’s readout of that call, which Trump has repeatedly characterized as “perfect,” omits some words and phrases that were said during call. Vindman said he tried to correct it but those changes were never made.

He will testify in an open hearing Tuesday morning at 9 am Eastern.

Jennifer Williams

Williams is a special adviser to Vice President Mike Pence for Russian and European affairs who worked in the State Department. She listened to the July 25 call between Trump and Zelensky, and reportedly told lawmakers in her testimony last week that the call was not a normal diplomatic call.

Lawmakers presumably asked Williams what, if anything, Pence might have known about Trump’s policy toward Ukraine. According to the whistleblower complaint, Trump insisted Pence cancel his plans to attend Zelensky’s inauguration in May. Secretary of Energy Rick Perry went instead.

She will testify, alongside Vindman, on Tuesday morning at 9 am Eastern.

Kurt Volker

Volker was the US special representative to Ukraine negotiations, tasked with working with America’s European allies as well as the Russians to negotiate an end to the Russian war in Ukraine.

A career foreign service officer, Volker took on the Ukraine job on a part-time, voluntary basis but eventually got caught up in the White House’s shadow foreign policy toward Ukraine spearheaded by Giuliani. Volker stepped down in September amid the brewing impeachment scandal.

The first witness to testify in the closed-door impeachment inquiry, Volker told House lawmakers in October that he’d tried to advance US interests while simultaneously working to dilute some of Giuliani’s influence. Yet text messages show that Volker was a willing participant — along with Sondland, Perry, and Giuliani — in the not-so-official efforts to pressure Ukraine to pursue investigations.

He will testify in an open hearing on Tuesday afternoon, starting at 2:30 pm Eastern.

Tim Morrison

Morrison joined the National Security Council when Bolton arrived at the White House and was briefly the top Ukraine official on the National Security Council, having taken over for Fiona Hill in July 2019. In his October testimony to the House Intelligence Committee, Morrison essentially confirmed the quid pro quo: that Trump wanted to withhold military aid to pressure Ukraine to investigate his political opponents.

Morrison did tell the committee he didn’t think Trump did anything illegal on the July 25 call with Zelensky, but he also said that at the time he feared if the details of the call were made public it could be politically explosive and weaken bipartisan support for Ukraine. Morrison resigned from his post at the NSC in October right before his scheduled deposition.

Morrison will testify alongside Volker on Tuesday afternoon at 2:30 pm Eastern.

Fiona Hill

From 2017 to July 2019, Hill was a senior director on the National Security Council responsible for coordinating US policy on Europe, including the European Union, NATO, Russia, Turkey, and Ukraine.

Hill resigned from her position in the White House by the time the July 25 Trump-Zelensky call occurred, but in her testimony she gave a firsthand account of a tense White House meeting that took place on July 10, in the days leading up to that phone call — a meeting that’s now key to the impeachment inquiry.

At that gathering, several senior US officials — including Hill, Bolton, Energy Secretary Rick Perry, and Ambassador to the EU Gordon Sondland — met with top aides to Ukrainian President Zelensky to discuss, among other things, a possible Trump-Zelensky meeting, which the Ukrainians had been pushing hard for but which Bolton and Hill were reluctant to agree to at that stage.

Hill sat in on that meeting, and she testified that during the sit-down, Sondland “blurted out” that there was already an agreement in place: Ukraine’s president would get a meeting with Trump if he agreed to launch certain “investigations in the energy sector” — which she said later became clear was code for Burisma, the Ukrainian gas company where Hunter Biden served as a board member.

Bolton, Hill said, reacted badly to Sondland’s announcement — abruptly ending the meeting and later telling her, in rather colorful terms, to report it to the NSC’s lawyer, John Eisenberg. “[Bolton] told me, and this is a direct quote,” Hill said, “‘You go and tell Eisenberg that I am not part of whatever drug deal Sondland and [acting White House Chief of Staff Mick] Mulvaney are cooking up on this.’”

She will testify in a public hearing on Thursday, beginning at 9:30 am Eastern.

David Holmes

Holmes is a counselor for political affairs at the US embassy in Kyiv, Ukraine. He overheard US ambassador to the EU Gordon Sondland’s call with Trump about “investigations” alongside Suriya Jayanti.

He is expected to testify Thursday, alongside Hill.

The witnesses who already testified

Marie Yovanovitch

Marie “Masha” Yovanovitch was the US ambassador to Ukraine between August 2016 and May of this year. A widely respected career diplomat and the highest-ranked female ambassador at the State Department, Yovanovitch was the target of Giuliani-led attacks falsely accusing her of, among other things, working to thwart President Trump’s Ukraine policy and being close to the previous Ukrainian president, Petro Poroshenko. That smear campaign ultimately led to her unceremonious dismissal months before her time was up.

As Vox’s Andrew Prokop explains, “Because Yovanovitch was ousted back in April, she can’t shed much light on the key allegations against Trump: that he pressured Ukraine’s new president, Volodymyr Zelensky, to investigate Joe Biden and his son in exchange for a White House meeting and withheld US military aid. All that unfolded after she left Kyiv.”

During her hearing last Friday, she withstood a real-time attack from Trump and made her case for how the president and his allies forced her out of her job as ambassador to Ukraine. What’s more, she said the administration’s actions may have increased corruption in Ukraine — not curbed it. As she departed the dramatic session, Yovanovitch received a rare standing ovation from onlookers.

William Taylor

William “Bill” Taylor is the current US chargé d’affaires for Ukraine — basically the acting ambassador at the US embassy in Kyiv. He took over for Ambassador Marie Yovanovitch in May after she was pushed out by top Trump officials who falsely believed she was disloyal to the president. Taylor also served as the US ambassador to Ukraine from 2006 to 2009.

In his closed-door deposition with congressional investigators last month, Taylor said his “clear understanding” of the White House’s position was that US military aid and other assistance wouldn’t go to Ukraine unless Ukrainian President Volodymyr Zelensky agreed to investigate Joe Biden and his son, Hunter. In other words, he believed there was a clearly proposed quid pro quo.

Taylor’s concerns about the White House’s Ukraine policy first came to light in text messages between him and two US diplomats in which Taylor expressed his worry that pushing the Ukrainians to open such an investigation would inappropriately involve that country in domestic US politics. The envoy, who in his testimony was very open about wanting the US to strongly support Ukraine, said he was worried that the aid-for-investigations ploy would hurt American-Ukrainian relations.

He reiterated all those points during Wednesday’s opening. He also dropped a bombshell, adding that he’d learned new information last week from a staff member about a previously unknown phone call involving Trump.

Taylor did not name the staff member but described that person’s account of going to a restaurant with Ambassador to the EU Gordon Sondland on July 26. The staffer witnessed Sondland call Trump and heard Trump ask Sondland, over the phone, about “investigations.” Sondland said the Ukrainians were ready to move forward with them.

It was later revealed that the staffer’s name is David Holmes, and will take part in a closed-door deposition on Friday — the same day as Yovanovitch’s hearing. It’s also been reported that a second US embassy official overheard Sondland’s call with the president.

George Kent

George Kent is the current deputy assistant secretary in the State Department’s European and Eurasian affairs bureau. In that senior role, he oversees the Trump administration’s policy toward Ukraine, as well as Moldova, Belarus, Georgia, Armenia, and Azerbaijan. Based in Washington, his job is to communicate with the US embassies in those countries and ensure that the administration’s policies are being properly carried out.

Perhaps more importantly, though, Kent also served as the senior anti-corruption coordinator in the State Department’s European bureau from 2014-15 — which means he has particularly good insight into how the US government normally goes about addressing issues of corruption in countries like Ukraine.

(Remember: Trump and his allies have argued that his demands of the Ukrainian president to investigate Biden and his decision to withhold US military aid from the country stemmed from his concerns over corruption in the country and had nothing to do with his own personal political interests.)

During his closed-door deposition, Kent explained to investigators why the White House’s “corruption” defense is bogus. “Politically related prosecutions are not the way of promoting the rule of law. They undermine the rule of law,” he said. He also detailed Rudy Giuliani’s “campaign of lies” against US ambassador to Ukraine Marie Yovanovitch, which ultimately resulted in her early recall from Kyiv.

Kent made these same points alongside William Taylor, the top US diplomat in Ukraine, during Wednesday’s first public impeachment hearing.

The rest of the impeachment cast of characters

US officials

John Bolton: Trump’s national security adviser from April 2018 to September 2019, he reportedly said he was concerned by what he described as the “drug deal” the administration was “cooking up” toward Ukraine.

However, it’s not clear how hard he tried to stop it. Bolton’s lawyers have said he is open to testifying publicly despite White House orders not to cooperate, but he is awaiting a court decision before agreeing to do so.

Catherine Croft: A State Department Ukraine expert who worked for former special envoy for Ukraine Kurt Volker. She told congressional investigators about calls she received pushing for Yovanovitch’s dismissal as ambassador.

John Eisenberg: The National Security Council’s top lawyer to whom multiple administration officials reported their concerns about the White House’s Ukraine policy. In their testimonies, staffers said he chose to put the transcript of the problematic July 25 Trump-Zelensky call into an ultra-secret server. He has also repeatedly concluded no one involved in the quid pro quo scheme violated the law, despite noting how unorthodox it all was.

Rudy Giuliani: The former mayor of New York City is a central figure in the impeachment scandal. In his capacity as President Trump’s personal lawyer, Giuliani spearheaded the campaign to convince the Ukrainian government to open an investigation into Joe Biden and his son. He was also instrumental in pushing the false allegations against Marie Yovanovitch that ultimately ended her stint as the US ambassador to Ukraine well before her assignment was up.

Suriya Jayanti: Jayanti is an economics officer at the US embassy in Kyiv, Ukraine. She overheard US ambassador to the EU Gordon Sondland’s call with Trump about “investigations” alongside David Holmes.

Charles Kupperman: Kupperman was Bolton’s No. 2 at the National Security Council. Kupperman was subpoenaed by House Democrats to testify, but he asked the courts to weigh in first as he had also received orders from the White House not to testify.

Kupperman, as deputy NSA, likely had an insider’s view on what was going on in the White House with respect to Ukraine. But House Democrats dropped the subpoena last week, making it unlikely Kupperman will testify anytime soon.

Michael McKinley: McKinley resigned from the State Department on September 30, where he’d previously served as a top aide to Secretary of State Mike Pompeo. McKinley explicitly said he stepped down over Pompeo’s failure to support or defend State Department personnel amid the impeachment inquiry. McKinley told House lawmakers that he wanted to put out a statement of support of Ambassador Yovanovitch but that that request was denied.

Mick Mulvaney: He is the acting White House chief of staff. Trump told him to tell the Office of Management and Budget to put a hold on aid to Ukraine. When confronted about it by reporters in October, he said this kind of thing happens “all the time” and told critics to “get over it.” (He later unsuccessfully walked back his statements.) Based on current testimony, it seems that Mulvaney was intimately familiar with the scheme to pressure Ukraine.

Rick Perry: The current secretary of the Department of Energy, Perry led the US delegation to Ukraine for Zelensky’s inauguration in May. Along with US ambassador to the EU Gordon Sondland and special Ukraine representative Kurt Volker, Perry was pretty bullish on Zelensky and urged Trump to work with him. His full role in the scandal isn’t clear — Perry hasn’t testified — but Trump has blamed Perry for getting him to set up the July 25 call with Zelensky.

Perry announced he would be resigning from his post as energy secretary in October but as of now he is still in the job.

Mike Pompeo: Pompeo is the secretary of state, though his role in l’affaire Ukraine is still a bit murky. Pompeo listened in on the July 25 call between Zelensky and Trump. Based on testimony so far, Pompeo allowed Giuliani’s shadow diplomacy with Ukraine to happen under his watch at State. Several former officials who’ve testified have also expressed their disappointment over Pompeo’s failure to publicly defend career diplomats like Yovanovitch, who became collateral in the Ukraine scheme.

Phillip Reeker: The acting assistant secretary in charge of European and Eurasian affairs at the State Department, Reeker testified to House lawmakers that he tried to defend Ambassador Yovanovitch against attacks from Trump’s political allies, specifically Giuliani. Reeker said he wanted the State Department to issue a statement of support for Yovanovitch, which ultimately didn’t happen.

Mark Sandy: The deputy associate director for national security programs at the Office of Management and Budget, Sandy told House investigators he received no explanation for why the White House froze the military aid to Ukraine. He found the decision to be highly irregular, informed by his many years working these issues at the OMB.

Ukrainian officials

Oleksandr Danylyuk: Ukranian President Volodymyr Zelensky’s former national security adviser — so essentially John Bolton’s counterpart in Ukraine through September. He took part in the July 10 White House meeting in which US Ambassador to the EU Gordon Sondland said investigations into the Bidens were important to President Trump.

Just 10 days later, Danylyuk relayed his concerns about Ukraine being used as a pawn in Trump’s reelection campaign to US Chargé d’Affaires for Ukraine Bill Taylor and US special envoy to Ukraine Kurt Volker.

Per Taylor, Danylyuk remained in close contact with US officials. In early September, Danylyuk mentioned to National Security Council director for European affairs Tim Morrison that he was concerned about dwindling US support for Ukraine.

Yuri Lutsenko: Ukraine’s now-former prosecutor general who helped plant the seeds for the conspiracy theories about Ukraine and about Ambassador Yovanovitch that fueled Giuliani’s actions.

This spring, Lutsenko (who was still the prosecutor general at the time) gave interviews to the publication The Hill in which he announced he was opening investigations into Ukraine’s meddling into the 2016 elections (this is a debunked conspiracy theory that alleges Ukraine worked with Democrats to frame Russia for election interference) and into Burisma, the company tied to Hunter Biden.

Lutsenko has since retracted many of his allegations and said there’s no reason to investigate the Bidens.

Igor Fruman: a Ukrainian associate of Rudy Giuliani. Fruman was arrested, along with Lev Parnas, in October on charges related to campaign finance violations tied to illegal donations to US political campaigns, including a pro-Trump super PAC. Parnas and Fruman also allegedly lobbied to get Yovanovitch removed from her post in Ukraine.

Lev Parnas: another Ukrainian associate of Giuliani’s. Parnas was arrested, along with Igor Fruman, in October on charges related to a campaign finance violations over illegal donations to US political campaigns, including a pro-Trump super PAC. Parnas and Fruman also reportedly began working with Giuliani in his campaign to get Ukraine to investigate the Bidens and to get Yovanovitch removed from her post.

Parnas is now saying through a lawyer that in May he traveled to Ukraine to tell the new administration that Vice President Mike Pence wouldn’t attend Zelensky’s inauguration unless the prosecutor investigated the Bidens. He said he did so at Giuliani’s instruction — something Giuliani has denied. There’s some doubt about how legitimate this story actually is as Fruman has also denied it.

Petro Poroshenko: the Ukrainian president who was ousted in 2019 after the election of Zelensky. The New York Times reported that, as Poroshenko faced grim reelection prospects, he became more receptive to pursuing the investigations that the Trump administration wanted: one into Burisma and the other into aspects of Ukraine’s role in the 2016 elections.

Viktor Shokin: Ukraine’s former top prosecutor who was fired in March 2016. Trump’s allies have falsely claimed that Vice President Joe Biden tried to get Shokin fired because he was investigating the Ukrainian natural gas company Burisma where Biden’s son Hunter served on the board. There’s a video of Biden discussing his efforts to push Shokin out, which Trump claims is proof of a conspiracy.

But Trump is wrong. When in power, Shokin was seen as an obstacle to cracking down on corruption in Ukraine, and the investigation into Burisma had actually languished during Shokin’s tenure. What’s more, Biden’s push to get Shokin fired wasn’t Biden’s idea — it was Obama administration policy that originated at the State Department. Other Western governments and international organizations also embraced the view that Shokin had impeded efforts to crack down on graft in Ukraine and should be fired.

Andriy Yermak: Yermak is a top adviser to Ukrainian President Volodymyr Zelensky, who features heavily in text messages released by the House in the impeachment probe between US State Department officials.

In July, Volker put Yermak in touch with Giuliani, and Yermak later met with Giuliani in Madrid. Yermak lobbied for a meeting between Zelensky and Trump. According to House testimony from Volker, Giuliani insisted that the Ukrainians commit to investigations and Zelensky announce publicly probes into Burisma and the 2016 elections before any such meeting could be set.

Volodymyr Zelensky: Zelensky was overwhelmingly elected president of Ukraine in April 2019. A former comedian, Zelensky had no political experience, though he literally played a president on TV. The newcomer rode a populist, anti-corruption message into office and in July won a majority in Ukraine’s parliament, known as the Rada, clearing the way for his agenda.

That parliamentary victory preceded the now-infamous July 25 phone call with Trump where the president asked Zelensky to “do us a favor though” and investigate the Bidens. Zelensky, an untested president dealing with a war with Russia in eastern Ukraine, needed US military assistance.

The central question of the impeachment investigation now is whether Trump, knowing this, withheld security aid to force Zelensky to pursue investigations into his political rivals.

Zelensky, for his part, has made it clear that he wants to stay out of the US political drama. Meeting with Trump on the sidelines of the United Nations in September, he said that Ukraine did not want to interfere in the US elections. “I think good phone call,” Zelensky told reporters of the July 25 conversation. “It was normal. We spoke about many things, and I — so I think and you read it that nobody pushed me.”