President Donald Trump has called it "a witch hunt," but special counsel Robert Mueller's Russia investigation has already resulted in seven guilty pleas and one conviction at trial, with a cast of defendants that include Trump's former campaign chairman, ex-national security adviser and onetime personal lawyer.

In all, 34 people and three companies have been criminally charged as a result of the probe. Mueller was named special counsel in May 2017 by Deputy Attorney General Rod Rosenstein, and directed to investigate "any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump" and "any matters that arose or may arise directly from the investigation."

Paul Manafort, Donald Trump's former campaign chief, arrives for a hearing at U.S. District Court in Washington on June 15, 2018. Brendan Smialowski / AFP - Getty Images file

Paul Manafort

He ran Trump's campaign for part of 2016 and was convicted in August on five counts of tax fraud, one count of failure to file a report of foreign bank and financial accounts and two counts of bank fraud. Prosecutors said he'd hidden millions of dollars overseas. Prosecutors had recommended he get up to 24 years, but he was sentenced to just 47 months in that case on Thursday. He pleaded guilty in a second case brought by the Mueller team in September, and is scheduled to be sentenced for those crimes on Wednesday.

Rick Gates leaves Federal Court on Dec. 11, 2017 in Washington. Brendan Smialowski / AFP - Getty Images file

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Rick Gates

Manafort's former business partner and Trump's former deputy campaign chair pleaded guilty to conspiracy and lying to Mueller's investigators about his business dealings with Manafort. Gates, who also worked on Trump's inaugural committee, has been cooperating with Mueller's investigation and testified against Manafort at his trial in Alexandria, Va. His sentencing has been repeatedly delayed. Prosecutors said in January that "Gates continues to cooperate with respect to several ongoing investigations."

Michael Cohen, President Donald Trump's former lawyer, speaks after testifying to the House Oversight and Reform Committee on Capitol Hill on Feb. 27, 2019. Pablo Martinez Monsivais / AP

Michael Cohen

Trump's longtime fixer pleaded guilty to lying to Congress about the duration of Trump's plan to build a Trump Tower in Moscow. He was sentenced to three years in prison for that plea and another in a case that had been brought by federal prosecutors in Manhattan, where he admitted to eight felony counts of tax evasion, bank fraud and campaign finance violations. He's scheduled to begin serving his sentence May 6.

Michael Flynn leaves federal court following his plea hearing on Dec. 1, 2017 in Washington. Chip Somodevilla / Getty Images file

Michael Flynn

A top Trump surrogate and foreign policy adviser during the 2016 campaign who admitted to lying to the FBI about the substance of his conversations with Russian ambassador Sergey Kislyak during his brief stint as national security adviser. He's expected to be sentenced later this year.

Former Trump campaign aide George Papadopoulos with his wife Simona Mangiante leaves after his sentencing hearing at U.S. District Court in Washington, on Sept. 7, 2018. Yuri Gripas / Reuters

George Papadopoulos

Another Trump foreign policy adviser, he pleaded guilty to making false statements to the FBI about the timing of his conversations with a professor who had ties to Russian intelligence. He'd said he'd spoken with the professor before he went to work for Trump, when it was afterward. The professor had told Papadopoulos that Russia had "thousands of emails" that would damage Trump rival Hillary Clinton's campaign. Papadopoulos was sentenced to 14 days in jail.

Alex van der Zwaan, left, arrives at Federal District Court in Washington on Feb. 20, 2018. Van der Zwaan has been accused of lying to investigators about his interactions with Rick Gates, who was indicted last year along with Paul Manafort, President Donald Trump's campaign chairman, on charges of conspiracy to launder money and acting as an unregistered foreign agent. Susan Walsh / AP file

Alex van der Zwaan

The London-based lawyer admitted to lying to Mueller's investigators about his contacts with Gates. Van der Zwaan had worked with Gates and Manafort for a Ukrainian political party that was closely allied with Russia. He was sentenced to 30 days behind bars and fined $20,000.

Richard Pinedo via LinkedIn

Richard Pinedo

He was sentenced to six months in federal lockup and six months of home confinement for selling bank account and other stolen identity information to a group of Russians accused of interfering in the election. The Russians allegedly used the information to create fake online identities. The California man has said he didn't know who his clients were, and Mueller's office has said he was cooperative with their investigators.