Former President Trump’s hush money trial kicked off in New York on Monday, marking the first criminal trial against a former or current U.S. president.

The Manhattan trial began with jury selection and is expected to feature a host of star witnesses, including former allies of Trump and those connected to the 2016 hush money payment to adult film star Stormy Daniels.

It comes after weeks of tensions and back-and-forth over an imposed gag order following Trump’s series of social media attacks against various expected witnesses and others related to the case.

Meet the key players in the case:

Donald Trump

The former president is accused of illegally covering up a hush money payment made to conceal an alleged affair ahead of the 2016 election.

He faces 34 counts of falsifying business records in connection with reimbursements to then-fixer Michael Cohen after he paid Daniels $130,000 in October 2016 to keep quiet about the alleged affair.

He has pleaded not guilty and repeatedly denied the affair.

The indictment, which was handed down more than a year ago, made Trump the first ex-president to ever face criminal charges. The former president was later charged in three other criminal cases and faces a total of 91 counts in four separate jurisdiction.

Michael Cohen

Cohen, Trump’s onetime personal lawyer, is at the center of the case’s allegations. He is expected to serve as a key witness against the former president, testifying about payments made to Daniels.

He pleaded guilty in 2018 to federal charges and was sentenced to three years in prison. The charges were in part related to the payments made to Daniels as part of a nondisclosure agreement, and he claimed he did so at the direction of “a candidate for federal office.”

Cohen was paid back by Trump, whose company logged the reimbursements as legal expenses.

The payments made by Cohen were part of a broader “catch-and-kill” scheme to quell negative coverage about Trump before the election, prosecutors argue.

Cohen was first introduced to Trump in 2006 by the former president’s eldest son, Donald Trump Jr., wile working at a law firm. Testifying in Trump’s civil fraud trial last year, Cohen said he had “admired” Trump since high school.

When the New York real estate mogul asked Cohen to leave his firm and join the team at the Trump Organization, Cohen agreed and became one of Trump’s closest aides.

Amid the fallout of his and Trump’s legal woes, Cohen has become one of the former president’s most vocal critics.

Stormy Daniels

Daniels, whose real name is Stephanie Clifford, claims she first met Trump in July 2006 at a golf tournament in Stateline, Nev., a town on the shores of Lake Tahoe.

She says Trump invited her to his hotel suite, they had a sexual encounter and he suggested she could be a contestant on “Celebrity Apprentice.” Trump has repeatedly denied having a sexual relationship to Daniels.

Daniels agreed to tell the story in May 2011 to In Touch Weekly magazine, which did not run the story after Cohen reportedly threatened to sue them. The article was eventually published in 2018, when reports of the alleged affair were made public.

Daniels tried to tell the story again in 2016, prompting the hush money payment by Cohen and the nondisclosure agreement less than two weeks before the 2016 election, prosecutors say.

She later sued Cohen in 2018 to avoid the nondisclosure agreement and later filed separate defamation suits against Cohen and Trump.

She is expected to testify in the trial, which is expected to last about six weeks.

Alvin Bragg

Manhattan District Attorney Alvin Bragg (D) was a leading force behind the criminal indictment against Trump, having decided last year to convene a New York grand jury that ultimately decided to charge the former president.

Becoming the first Black district attorney in 2022, Brag inherited the hush money investigation from former Manhattan District Attorney Cyrus Vance Jr., who retired.

Prior to his time in the DA’s office, Bragg served as an assistant U.S. attorney for the Southern District of New York and an assistant attorney general for New York.

Judge Juan Merchan

Merchan is the New York Supreme Court judge overseeing the trial.

Tensions between him and the former president’s legal team have ramped up in recent weeks, following a gag order Merchan placed and expanded after Trump attacked his wife and daughter on social media.

Trump has repeatedly claimed Merchan is corrupt, and his legal team has demanded he step aside over his daughter’s employment at a firm that works for high-profile Democrats.

Merchan declined the latest effort to recuse himself from trial shortly before it started Monday.

He has years of experience working in the New York City court system and worked as an assistant attorney general in-charge in Nassau County and Suffolk County in the early 2000s. Since 2009, he has served as an acting justice on the state Supreme Court, where he presides over felony criminal trials.

He previously oversaw a criminal tax fraud trial against the Trump Organization, in which the company was fined more than $1 million after being convicted on 17 counts.

Karen McDougal, David Pecker

McDougal, a former Playboy model, is expected to testify in the trial. She claims she had sexual relations with Trump, which Trump has denied.

Pecker, the former chair of American Media Inc., which publishes the National Enquirer, could also testify as a witness.

Prosecutors alleged Pecker, a longtime ally of Trump, would purchase the rights to certain stories potentially embarrassing to him. Pecker and American Media Inc. were accused of participating in a “catch-and-kill” scheme, which included an alleged payment to McDougal for the rights to her story. The company never published McDougal’s story.

Trump’s legal team: Todd Blanche, Susan Necheles

A former federal prosecutor for the Southern District of New York, Blanche is Trump’s lead counsel.

He left his position as a partner at Cadwalader, Wickersham & Taft, an elite New York law firm, in April to represent Trump and has experience involving white-collar crimes.

Necheles has been a central member of Trump’s legal team in New York in recent years, CBS News reported. She has represented organized crime figures and several Democratic politicians, the outlet added.

Trump aides

A few of Trump’s former White House aides could potentially be witnesses at the trial.

Those include former White House communications director Hope Hicks, who was once one of Trump’s closest aides and served as his campaign press secretary ahead of the 2016 election. She was interviewed by prosecutors for the case last year, and her attorney previously said she was unaware of the payments.

Former Trump aide Kellyanne Conway could also testify, Axios reported, along with Rhona Graff, who served as senior vice president at the Trump Organization.