WASHINGTON (NewsNation) — Jack Smith, the federal prosecutor who is leading the Jan. 6 investigation into former President Donald Trump, told reporters that the Capitol riots were an attack on American democracy, fueled by lies.

Smith unveiled a four-count indictment against Trump Tuesday evening, charging him with conspiracy to defraud the U.S., among other charges. On Thursday afternoon, Trump will be formally arraigned in Washington, D.C.

With a long history of prosecuting crimes ranging from terrorism to white-collar offenses, Smith has built a reputation for winning tough cases against corrupt politicians, war criminals, mobsters and crooked cops.

Smith is leading two parallel criminal probes against Trump: One of the two investigations involved Trump’s handling of classified documents he retained after leaving the White House in January 2021. The second — which Trump will be arraigned for on Thursday — examined efforts to overturn the results of the 2020 U.S. election that the former president lost, including a plot to submit phony slates of electors to block Congress from certifying Democrat Joe Biden’s victory.

Appointed last November by Attorney General Merrick Garland to take over two Justice Department investigations involving Trump, Smith made history as the first federal prosecutor – though not the first prosecutor – to secure not one, but two indictments against a current or former U.S. president.

“I appointed Jack Smith, special counsel, to take on the ongoing investigation in order to underline the department’s commitment to accountability and independence,” Garland said.

Manhattan District Attorney Bragg in April charged Trump with 34 felony counts of falsifying business records involving hush money paid to a porn star before the 2016 U.S. election.

When Smith is not busy competing in Ironman swim-cycle-run triathlon races, according to his former colleagues, he is working as a dogged investigator who is open-minded and not afraid to pursue the truth. They described him as just as tenacious in seeking to have criminal charges dropped for the innocent as he is to win convictions of the guilty.

“If the case is prosecutable, he will do it,” said Mark Lesko, an attorney at the firm Greenberg Traurig LLP who worked with Smith when both were prosecutors at the U.S. Attorney’s Office in New York. “He is fearless.”

However, this case is unlike any other that Smith has brought because of who is being charged. Trump served as president from 2017 to 2021 and is now seeking to return to the White House, leading a crowded field of candidates seeking the 2024 Republican presidential nomination.

“My office will seek a speedy trial so that our evidence can be tested in court and judged by a jury of citizens. In the meantime, I must emphasize that the indictment is only an allegation and that the defendant must be presumed innocent until proven guilty,” Smith said.

But critics of the special counsel say Smith is “overzealous” in his prosecutions, adding that quality has cost him some high-profile cases during his career.

So, who exactly is Jack Smith?

Smith, a Harvard Law School grad who is not registered with any political party, started as a prosecutor in 1994 at the Manhattan District Attorney’s Office under Robert Morgenthau, who was best known for prosecuting mob bosses.

In 1999, Smith started working at the U.S. Attorney’s Office in Brooklyn.

Smith also won a murder conviction against Ronell Wilson, a drug gang leader who murdered two undercover New York City police officers, though a federal appeals court vacated the death penalty verdict.

In 2008, Smith left to supervise war crime prosecutions at the International Criminal Court in The Hague. He returned to the Justice Department in 2010 to head its Public Integrity Section until 2015, a team tasked with prosecuting public officials accused of criminal misconduct.

Some cases resulted in convictions, including former Arizona congressman Rick Renzi, who served nearly two years in prison for extortion and money laundering before being pardoned by Trump.

Other cases ended in mistrials or were overturned, like when former Virginia Gov. Bob McDonnell was initially convicted of receiving gifts in exchange for political favors, which was later thrown out by the Supreme Court.

The unit also failed to convict former Senator and vice presidential candidate John Edwards, who was accused of illegally using campaign cash to hide an affair with his mistress. Edwards’ case ended in a mistrial.

More recently, Smith returned to war crimes cases in The Hague, winning the conviction of Salih Mustafa, a former Kosovo Liberation Army commander who ran a prison where torture took place during the 1998-99 independence conflict with Serbia.

Smith was also involved in the prosecution of Charles Schwarz, one of several former New York City police officers who were implicated in a high-profile police brutality case involving Abner Louima, a jailed Black inmate who had been assaulted by police with a broomstick.

Trump’s team used Smith’s legal record to attack the prosecutor on social media and most recently at a rally in Pennsylvania.

“This deranged lunatic named Jack Smith, who’s been overturned unanimously by the Supreme Court, he’s tried to destroy many lives,” Trump said.

While his detractors may want to focus on some of the missteps, Smith has a reputation for winning some tough cases.

Reuters contributed to this report.