By Madeline HalpertBBC News
Getty ImagesFulton County District Attorney Fani Willis has told US media she is carrying out the Trump probe as she would any other caseFulton County's first female district attorney is facing the possibility of being kicked off the highest-profile case of her career - prosecuting Donald Trump - because of her relationship with a man she hired to work on the case.
Fani Willis was preparing to start her new role as Fulton County District Attorney in Georgia when Donald Trump made a phone call to a top Republican in the state that would upend her work for the next several years.
On 2 January 2021, the former president phoned Georgia Secretary of State Brad Raffensperger and asked him to "find 11,780 votes", the number he needed to beat Joe Biden, who had won the state and the 2020 presidential election several weeks before.
Audio from the call was leaked to US media the next day, whipping up a massive political and legal storm on Ms Willis's first day in office.
"How soon I knew an investigation may be warranted was on day one," Ms Willis told USA Today in 2022.
Two-and-a-half years after that phone call, on 14 August 2023, a grand jury in Fulton County voted to charge Mr Trump and 18 others with attempting to overturn the election result in the state.
Mr Trump's lawyers called the indictment "shocking and absurd".
Fani Willis is known by fellow Georgia lawyers and those who have worked with her as a dogged prosecutor capable of securing convictions in high-profile and complex cases.
"She had a reputation of always being prepared," said Melissa Redmon, who worked in the Fulton County District Attorney's office at the same time as Ms Willis. "Given the type of cases she prosecuted, that took a tremendous amount of dedication."
Watch: 'I make decisions based on the facts and the law.'Ms Willis used that rigour in a controversial Atlanta Public Schools scandal involving officials who cheated to improve standardised test scores, and in prosecuting several well-known rappers accused of gang crimes. She has insisted that in investigating Mr Trump, her office followed the same procedures it would use to look into any reports of a possible crime.
"The reality is, we have a job, and the job is just to try to find the truth," she told the New York Times in February. "We're just going to do that [Trump] case like every other."
But now the sprawling and historic case is under threat because of accusations of impropriety, after it was revealed Ms Willis had an affair with Nathan Wade, a lead prosecutor on the case.
One of Mr Trump's co-defendants is pushing a judge disqualify her and drop some of the charges, saying the case is tainted.
The first female Fulton County DA
Born in Inglewood, California in 1971, Ms Willis was raised primarily by her father, a criminal defence lawyer and member of the Black Panthers, the radical political party that championed black civil rights.
She graduated from the historically black college Howard University in 1993, before receiving a law degree from Emory University in Georgia in 1996.
Just five years later, Ms Willis joined the Fulton County District Attorney's office, where she served in several different divisions until 2018.
During her nearly two decades there, Ms Willis led more than 100 jury trials, including the longest criminal trial in Georgia history. It ended with convictions for 11 of 12 Atlanta public school officials accused of cheating on state-administered standardised tests in 2009 for better bonuses and promotions.
Her successful trials quickly secured her a reputation of being an exceptionally skilled prosecutor, even among the accused, said Ms Redmon. During her time at the DA's office, Ms Redmon remembers hearing a defendant once plead with a relative to try to get a witness to leave town because the prosecutor tackling their case, Ms Willis, was "a genius".
In 2020, after years in private practice, Ms Willis decided to go head-to-head with her former boss, six-term Fulton County District Attorney Paul Howard.
She won in a runoff election with 73% of the votes, becoming the first black woman to serve as Fulton County's top prosecutor.
The probe against Trump
Ms Willis launched the investigation into Mr Trump's post-election conduct just a month after his infamous phone call to Mr Raffensperger.
Her office interviewed dozens of witnesses, including top Georgia Republican officials like Governor Brian Kemp and Mr Raffensperger as well as Mr Trump's former lawyer Rudy Giuliani.
Mr Trump repeatedly lambasted the investigation on his account on the Truth social media platform.
The "Radical Left Democrat 'Prosecutor' from Georgia who is presiding over one of the most Crime Ridden and Corrupt places in the USA, Fulton County, has put together a Grand Jury to investigate an absolutely 'PERFECT' phone call to the Secretary of State", he wrote in 2022.
Ms Willis had a come-back to the attacks: no one is above the law.
"I do not have the right to look the other way on a crime that could have impacted a major right of people in this community and throughout the nation," she told the New York Times last September, referring to the right to vote.
The accusations against Ms Willis
Ms Willis is now facing accusations that have the potential to derail her case, and her reputation.
One of Mr Trump's co-defendants, Michael Roman, has asked a judge to dismiss her from the case, alleging she had an "improper" relationship with Mr Wade.
Mr Roman has alleged the two took luxury trips together, paid for with money Mr Wade earned from his work on the probe.
Ms Willis has admitted to the relationship, but has asserted allegations of impropriety were unfounded and had no bearing on the case.
The two did travel together, but split expenses equally, she said.
Soon after Mr Roman shared evidence of the relationship in court filings, Georgia's legislature launched an investigation into possible misconduct by Ms Willis.
Judge Scott McAfee, who is overseeing the Trump case, will hold a hearing on 15 February to weigh whether the relationship has, essentially, tainted the case. Ms Willis asked him to dismiss the hearing, but he declined.
With additional reporting from Kayla Epstein
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