Donald Trump's former lawyer Michael Cohen, who was once Trump's confidant and self-described "fixer," is set to return to a courtroom in New York as the star witness in the former president's $250 million civil fraud trial.

Cohen spent a decade in Trump's inner circle before becoming ensnared in his own legal problems, resulting in prison time and disbarment -- during which time he flipped to become one of Trump's most vocal critics.

Trump is expected to attend the trial on Tuesday, which would likely mark the first time they've seen each other in person in five years.

"It appears that I will be reunited with my old client @realDonaldTrump when I testify this Tuesday, October 24th at the @NewYorkStateAG civil fraud trial. See you there!" Cohen wrote on Twitter, now known as X, on Friday.

Cohen's testimony could also provide an opportunity for him to come full circle. His 2019 congressional testimony claiming that Trump inflated his net worth led New York attorney general Letitia James to open her investigation into the former president.

Trump has denied all wrongdoing in the case and has appealed a pretrial ruling from the judge that already found him liable for defrauding banks and insurers.

“We have a corrupt legal system in our country,” Trump said last week before entering court.

Cohen's testimony was previewed as critical evidence during the state's opening statement earlier this month.

"[Trump] wanted to be higher on the Forbes list, and he then said 'I'm actually not worth $6 billion. I'm worth seven. In fact, I think it's actually now worth eight, with everything that's going on,'" Cohen said in a portion of his deposition that was played during the state's opening statement.

"Allen and I were tasked with taking the assets, increasing each of those asset classes, in order to accommodate that $8 billion number," Cohen said in his deposition, referring to then-Trump Organization CFO Allen Weisselberg, who pleaded guilty to tax evasion charges last year.

In 2018, Cohen pleaded guilty in two separate criminal cases and eventually spent more than 13 months in prison -- issues that are likely to be raised by Trump's attorneys to damage Cohen's credibility.

Cohen was initially scheduled to testify last week but postponed due to an ongoing medical issue. Trump still attended court for two days last week and instead watched testimony from his former accountant and an appraiser, in lieu of Cohen.

"Cohen didn't have the guts [to testify]," Trump told reporters last week during a break.

Trump's 'pit bull'

Cohen began working with Trump in 2007, eventually serving as a Trump Organization executive vice president, special counsel, and self-described legal "pit bull" for Trump.

"It means that if somebody does something Mr. Trump doesn't like, I do everything in my power to resolve it to Mr. Trump's benefit," Cohen told ABC News in 2011. "If you do something wrong, I'm going to come at you, grab you by the neck and I'm not going to let you go until I'm finished."

Cohen continued vehemently representing Trump as his boss ascended to the presidency, telling Vanity Fair in 2017 that he "would take a bullet for the president."

However, Cohen's dedication to Trump appeared to diminish after an April 2018 FBI raid of Cohen's home and office based on a referral from special counsel Robert Mueller as part if his probe into Russian interference in the 2016 election.

By August 2018, Cohen had pleaded guilty to eight criminal counts including tax evasion, campaign finance violations, and making false statements. Cohen also pleaded guilty to one count of making false statements to the United States Congress in November 2018.

'I helped him do it'

As part of his guilty plea, Cohen said he made illegal campaign contributions "in coordination and at the direction of a candidate for federal office" who his lawyer later identified as Trump. Those campaign violations related to hush money payments would later resurface in Trump's criminal indictment by Manhattan District Attorney Alvin Bragg.

Cohen was sentenced to three years in prison, was ordered to pay $1.39 million in restitution, forfeited $500,000, and was fined $100,000. He spent more than 13 months in federal prison before completing his sentence on home confinement during the COVID-19 pandemic.

Before he reported to prison in 2019, Cohen's testimony before the House Oversight Committee sparked James' investigation into Trump's finances.

"It was my experience that Mr. Trump inflated his total assets when it served his purposes, such as trying to be listed amongst the wealthiest people in Forbes, and deflated his assets to reduce his real estate taxes," Cohen testified.

Since his guilty pleas, Cohen has also written two books about his work with Trump, who briefly sued Cohen for $500 million before dropping the suit on the eve of his fraud trial.

"Over the years he had screwed people over, manipulated them and used them, and I helped him do it," Cohen wrote in his book "Revenge."

Cohen and the 'Team of Four'

Cohen's testimony at the fraud trial is likely to focus on Cohen's time in Trump's inner circle between 2011 and 2018, based on the timeframe of conduct alleged in state's case.

When Cohen testified before Congress, he provided Trump's financial statements between 2011 and 2013 to demonstrate that Trump used the statements to lower his tax burden while burnishing his net worth. The same statements have been entered into evidence in the fraud trial.

"I believe these numbers are inflated," Cohen testified about the documents, which he said were also used to obtain favorable insurance policies -- an area where Cohen appears to have personal experience.

Along with three other Trump Organization executives, Cohen served as a part of a "Team of Four" to review Trump's insurance policies in 2013, according to an email already entered into evidence.

"The Trump Organization has created a 'Team of Four' to review The Trump Organization's insurance program, insurance policy buying decisions, claims management and risk protection protocols," the email said.

Cohen's broad overview of "coverage terms & conditions" in the Team of Four suggests his testimony might provide new details about what the attorney general has alleged was a long-running scheme to use fraudulent financial documents to provide higher insurance limits and lower premiums.

Compared to former Trump Organization executives Allen Weisselberg and Jeffrey McConney -- co-defendants in the case whose testimony was marked by a lack of recall on certain issues -- Cohen is not adverse to testifying.

"I look forward to testifying and correcting the record as to the multiple misstatements and responses by previous witnesses who stated ... 'I don't recall.' Unfortunately for them, I do," Cohen told ABC News last week.