Rudy Giuliani, President Donald Trump’s personal lawyer, has relied on former Ukrainian officials and parliament members to try to unearth dirt that would help his client in the White House, an effort at the heart of Trump's impeachment.

All of them have controversial reputations in their home country, and several are now in the political wilderness. Most of them have ties to pro-Russian political figures or oligarchs, and appear eager to burnish their political clout by ingratiating themselves with allies of the American president.

Here is a short guide to the Ukrainians who Giuliani has met with or cited as key sources, as well as a few of the oligarchs exerting influence in the country. Giuliani met with several of these contacts in a trip to Budapest and Kyiv earlier this month for a documentary series produced by One America News network, which regularly features pro-Trump stories.

Andrii Artemenko

Ukrainian lawmaker Andrii Artemenko in 2017. Valentyn Ogirenko / REUTERS

Artemenko is a former member of parliament aligned with a pro-Russian faction. He was accused by Ukrainian authorities of proposing a deal to temporarily “lease” the Crimean peninsula to Russia. In January 2017, he met with Trump’s former lawyer Michael Cohen and a Trump supporter, Russian-born businessman Felix Slater, to discuss the plan aimed at eventually lifting U.S. sanctions on Russia. He also claimed to have evidence of corruption on former Ukrainian president Poroshenko. He told the New York Times in 2017 that he had received encouragement for his plans from aides to Russian President Vladimir Putin.

Andrii Derkach

Ukrainian lawmaker Andrii Derkach and President Donald Trump's personal lawyer Rudolph Giuliani show a document during a meeting in Kiev in this picture obtained from social media. Courtesy of Andriy Derkach via Reuters

Derkach is a member of the pro-Russian Party of Regions. He promoted the conspiracy theory that Ukraine interfered in the 2016 U.S. election. Derkach studied at the Russian FSB intelligence service (formerly KGB) academy in Moscow in the 1990s. His party backed the ousted pro-Russian president Viktor Yanukovych, who was forced from power amid street protests in 2014. He supported “anti-protest” laws restricting civil liberties.

Andriy Telizhenko

Ukrainian former diplomat Andriy Telizhenko and Rudolph Giuliani pose for a picture during a meeting in Kyiv on Dec. 5, 2019. Courtesy of Andrii Telizhenko via Reuters

Telizhenko is a former low-ranking official at the Ukraine embassy in Washington. He was quoted in a Politico article in January 2017 alleging a Democratic National Committee consultant contacted him and others at the embassy to unearth dirt on Trump and his campaign chairman, Paul Manafort. Others at the embassy deny his account. He has never released any documents or other proof of his allegations. Nearly three years later, he has been invited to meet senior Republican senators to discuss his claims. Telizhenko also worked for two chief prosecutors with controversial reputations: Yarema Vitaliy, who was accused of failing to go after those who shot at and killed pro-Western demonstrators in 2014; and Viktor Shokin (see below), who was sharply criticized by U.S. and European governments for his handling of corruption cases. Telizhenko met Giuliani through the former mayor’s friend, Victoria Toensing in 2016. He told NBC News he traveled with Giuliani from Budapest to Kyiv this month, helping with the documentary series for the conservative One America News network that portrayed the impeachment inquiry against President Trump as a witch hunt.

Oleksandr Dubinsky

Oleksandr Dubinsky in July 2019. Pavlo Gonchar / LightRocket via Getty Images

Dubinsky is a member of parliament from President Volodmyr Zelenky’s party. He's also a TV presenter accused of doing the bidding of Ihor Kolomoisky, a Ukrainian oligarch who says he is under investigation by U.S. authorities. Dubinsky has promoted the debunked allegation that Ukraine interfered in the 2016 election. He has accused former U.S. ambassador Marie Yovanovitch and Hillary Clinton’s 2016 campaign of orchestrating the publication of the so-called “black ledger” that implicated Trump’s campaign manager Paul Manafort. But Yovanovitch arrived for her post in Kyiv after the release of the documents. Manafort was sentenced to seven and a half years in prison by a federal court on bank and tax fraud. Bank wire transfers and other evidence confirmed the payments made to Manafort. Dubinsky met with Giuliani during his Dec. 4 trip to Ukraine, according to Telizhenko.

Kostiantyn Kulyk

Prosecutor Kostiantyn Kulyk at a news conference in Kiev on April 11, 2019. Viacheslav Ratynskyi / Reuters file

Kulyk is a former prosecutor whose career was dogged by corruption allegations. He was charged in 2016 with illicit enrichment for having assets far surpassing his salary. Yet, Kulyk remained a top prosecutor. He compiled a dossier in English accusing Hunter Biden of corruption due to his work on the board of the Burisma energy company. He alleged without offering evidence that Biden agreed to help the Ukrainian authorities cultivate relations with the Trump administration for a bribe. Kulyk was ultimately fired on Nov. 25, for failing to show up for mandatory vetting. His former boss in the military prosecutor's office told local media Kulyk had admitted in his security clearance application that he was friends with a suspected Russian intelligence agent in his home town of Kharkiv. Investigators also found that Kulyk's car was registered in the name of the commander of pro-Russian forces in eastern Ukraine.

Viktor Shokin

Prosecutor General of Ukraine Viktor Shokin speaks at a news conference in Kyiv in 2015. Sergii Kharchenko / NurPhoto via Getty Images

Shokin is a former prosecutor general. He was accused of blocking prosecutions linked to the shooting of demonstrators by special police forces in the 2014 Maidan protests and later, as chief prosecutor, dropped cases involving former pro-Russian president Viktor Yanukovych. Western governments, including the Obama administration, demanded he be replaced for failing to prosecute corruption cases, and then Vice President Joe Biden pushed hard for the change. Shokin alleges he was ousted because Biden wanted to prevent him from investigating Burisma and Hunter Biden. But a deputy prosecutor working under Shokin has said the Burisma case had been dormant at the time the U.S. was pushing for Shokin’s removal. Shokin made the allegation in a Sept. 4 affidavit requested by lawyers for the Russian-linked oligarch Dmitry Firtash (see below), who is fighting extradition to the United States on charges of bribery and racketeering. Giuliani has repeatedly cited the affidavit as a key piece of evidence, waving it around on camera, but without mentioning its origins. Shokin met with Giuliani on Dec. 4.

Yuriy Lutsenko

Prosecutor General of Ukraine Yuriy Lutsenko speaks at a trial in Kyiv in 2017. Danil Shamkin / NurPhoto via Getty Images file

Lutsenko is a former prosecutor general who was a key figure early on for Giuliani’s effort to shift attention to Ukraine’s alleged role in the 2016 election and the Biden family. Lutsenko, who succeeded Shokin, clashed with the former U.S. ambassador Marie Yovanovitch over his office’s investigations into anti-corruption activists. He initially cooperated with Giuliani, as he said he hoped the former mayor would help him get a meeting with U.S. Attorney General William Barr. But Lutsenko became a political lame duck after President Petro Poroshenko was defeated in a landslide by Volodymyr Zelenksy in the April presidential elections. He appeared less willing to cooperate with Giuliani, and later told Bloomberg News that there was no evidence of wrongdoing by Hunter Biden related to Burisma. He told the New Yorker he was not ready to cross a line and announce an investigation into the Bidens, despite demands from Giuliani. Lutsenko was replaced in August. He met Giuliani in Budapest this month as part of the One America News documentary.

Nazar Kholodnytsky

Ukraine's Anti-Corruption Prosecutor Nazar Kholodnytsky speaks to The Associated Press in Kiev in 2016. Efrem Lukatsky / AP file

Kholodnytsky is Ukraine’s special anti-corruption prosecutor. Last May, he met with Giuliani in Paris with the former mayor’s associates, Lev Parnas and Igor Fruman, who face charges of funneling foreign money into the upcoming U.S. election. Kholodnytsky was caught on tape coaching witnesses in corruption cases on how to avoid prosecution. He says the audio was taken out of context. Former U.S. ambassador to Ukraine, Marie Yovanovitch, cited the wiretaps when she called for his replacement in March. Kholodnytsky has said he has doubts about the case against former Trump campaign chairman Paul Manafort, and that the case on the Burisma energy company should be re-opened, something Giuliani has pushed for.

Gennady Kernes

Kharkiv Mayor Gennady Kernes in 2015. Sergey Kozlov / Sputnik via AP file

The mayor of Kharkiv is one of Giuliani’s first contacts in Ukraine. He was a member of Yanukovych's pro-Russian party but switched his allegiances after Yanukovych was ousted. Kernes is also an ally of the oligarch Pavel Fuchs, who negotiated with Trump over a possible Moscow hotel. Kernes survived an assassination attempt that same year. He was investigated over alleged embezzlement and allegedly abducting and torturing pro-Western protesters in the city, but thecase was later dismissed.

Oligarchs linked to Giuliani’s effort:

Dmytro Firtash

Dmitry Firtash, the Ukrainian billionaire, outside the Group DF office in Vienna, Austria, on March 14, 2016. Simon Dawson / Bloomberg via Getty Images

Firtash is an energy tycoon with deep ties to Russia and the Russian state-owned energy giant Gazprom. He's fighting extradition to the United States on bribery and racketeering charges. Firtash hired two former colleagues of Giuliani and Trump supporters, Victoria Toensing and Joseph diGenova, for his legal team. Parnas allegesGiuliani offered help with Firtash’s U.S. legal problems in exchange for helping with the hunt for compromising information on the Bidens. Just this week, federal prosecutors revealed that Parnas received a $1 million loan from a lawyer for Firtash. Giuliani obtained a sworn affidavit made by former prosecutor Shokin for Firtash's legal defense. Giuliani has waved the affidavit around on television, without mentioning the origins of the document. Firtash's money making schemes in Ukraine's gas market have beenthreatened by reform efforts that were backed by the former U.S. ambassador Marie Yovanovitch and the American embassy in Kyiv.

Ihor Kolomoisky

Ukrainian business tycoon Ihor Kolomoisky in 2019. Valentyn Ogirenko / Reuters file

Kolomoisky is a billionaire oligarch who owns the television station that broadcast the television series starring Zelensky, who was a comic before he was elected president. Kolomoisky says he is under investigation by the FBI. He was for a time an outspoken critic of Russia who helped fund and arm fighters waging war against pro-Russian separatists in eastern Ukraine. But he now advocates cooperating with Moscow because he says the West/US/NATO are not ready to help Ukraine. Kolomoisky initially refused to help Parnas and Fruman when they approached him in Israel but he now speaks about them positively. Kolomoisky has demanded the return of a bank he co-owned, PrivatBank, which was seized from him in 2016 amid charges of embezzlement. Kolomoisky denies the charges. The IMF has made clear to Zelensky’s government that it would not approve a loan package if PrivatBank was given back to Kolomoisky, Western officials say. His partners have hired a New York lawyer, Marc Kasowitz, who has worked for Trump.

Pavel Fuchs

Fuchs is a Ukrainian oligarch who amassed his wealth in Moscow in the 1990s and 2000s. Giuliani says Fuchs hired his company to update the emergency response system for the city of Kharkiv in 2017. Fuchs tried to get a Trump Tower built in Moscow 10 years ago, but it never materialized. Telizhenko, the former official in the Ukraine embassy in Washington who alleges Ukraine interfered in the 2016 election, says he has done consultant work for Fuchs.