The appointment of a special counsel to oversee the Justice Department’s probe of Hunter Biden is bringing renewed attention to the role such prosecutors have played in modern American history.

On Friday, Attorney General Merrick Garland tapped David Weiss, the U.S. attorney in Delaware who has been probing the financial and business dealings of the president’s son, to oversee the department’s investigation. He said Weiss asked to be appointed to the position and told him that “in his judgment, his investigation has reached a stage at which he should continue his work,” now as special counsel.

In January, Garland appointed Robert Hur, a former U.S. attorney in Maryland, to oversee the department’s investigation into how several batches of documents marked as classified ended up at Joe Biden’s Delaware home and at the offices of the president’s Washington think tank.

And last year, Garland appointed former Justice Department public corruption prosecutor Jack Smith to lead investigations into the retention of classified documents at former President Donald Trump’s Florida estate, Mar-a-Lago, as well as key aspects of a separate probe involving the Jan. 6, 2021, insurrection and efforts to undo the 2020 election. Trump is now facing charges in both cases.

A look at the origins of the special counsel, the position’s powers, and what to expect as Weiss pursues his work:

WHAT EXACTLY IS A SPECIAL COUNSEL?

A special counsel is an attorney appointed to investigate, and possibly prosecute, a case in which the Justice Department perceives itself as having a conflict or where it’s deemed to be in the public interest to have someone outside the government come in and take responsibility for a matter.

According to the Code of Federal Regulations, a special counsel must have “a reputation for integrity and impartial decisionmaking,” as well as “an informed understanding of the criminal law and Department of Justice policies.”

Though they’re not subject to the day-to-day supervision of the Justice Department, special counsels must still comply with department regulations, policies, and procedures. They also technically report to the attorney general – the one government official who can fire them.

The attorney general is entitled to seek explanations from a special counsel about any requested investigative or prosecutorial step, but under the regulations is also expected to give great weight to the special counsel’s views. In the event the attorney general rejects a move the special counsel wants to make, the Justice Department is to notify Congress at the end of the investigation.

WHAT POWERS DO THEY HAVE?

Special counsels are provided with a budget and can request a staff of attorneys, both inside and outside the department, if they need extra help.

In addition to the ability to bring indictments, special counsels are vested with bread-and-butter law enforcement tools such as the power to issue subpoenas and search warrants. Robert Mueller, a former FBI director who as special counsel in the Trump administration led the investigation into possible coordination between Russia and the 2016 Trump campaign, issued more than 2,800 subpoenas and executed nearly 500 search-and-seizure warrants.

HOW DO INDEPENDENT COUNSELS DIFFER FROM SPECIAL COUNSELS?

The position of special counsel differs in key ways from the work of independent counsels, who used to operate outside the supervision of the Justice Department and who led significant investigations in the post-Watergate era into administrations of both political parties.

One such independent counsel was Lawrence E. Walsh. During the Iran-contra affair in President Ronald Reagan’s second term, Walsh was appointed to probe secret arms sales to Iran and the diversion of money to rebel forces fighting the Nicaraguan government.

A decade later, independent counsel Ken Starr investigated fraudulent real estate deals involving a longtime associate of President Bill Clinton and first lady Hillary Clinton, delved into the removal of documents from the office of deputy White House counsel Vincent Foster after his suicide, and assembled evidence of Clinton’s sexual encounters with former White House intern Monica Lewinsky. As a result, Clinton was impeached by the House but survived a Senate trial.

But because of concerns over the cost and sprawling nature of such probes, Congress in 1999 permitted the provision governing independent counsels to expire.

The Justice Department then created new special counsel regulations, designing a position with intentionally less autonomy for circumstances in which the department feels it has a conflict of interest or wants to avoid becoming excessively entangled in politically sticky matters – like the current Trump-related probes.

Mueller was appointed in 2017 to investigate Russian election interference, a two-year probe that yielded criminal charges against 34 people, including several Trump associates, and three business entities. Mueller did not allege a criminal conspiracy between the Trump campaign and Russia. Though Mueller did not conclude whether Trump obstructed justice, he also did not exonerate him.

Weeks before Attorney General William Barr left office, he gave John Durham, then the top federal prosecutor in Connecticut, the title of a special counsel to ensure that he could continue investigating the origins of the Russia probe under new Democratic Justice Department leadership. In May, Durham released his findings in the form of a 300-page report showing that the FBI rushed into its investigation of ties between Russia and Trump’s 2016 campaign and relied too much on raw and unconfirmed intelligence.

WHO IS SPECIAL COUNSEL DAVID WEISS?

Appointed by Trump, Weiss was sworn in as Delaware’s U.S. attorney in 2018, according to his official biography. He was retained after Biden took over the presidency so he could continue to oversee the Hunter Biden investigation.

Before that, Weiss clerked for a justice on the Delaware Supreme Court. He was a federal prosecutor before going into private practice, where he focused on commercial litigation. After a stint with a financial services firm, he rejoined the Justice Department in 2007.

In his current position, Weiss has been leading the federal government’s investigation into Hunter Biden’s financial and business dealings. As special counsel, he will have broader authority to conduct a more sweeping investigation across various areas.

In June, Hunter Biden was charged with two misdemeanor crimes of failure to pay more than $100,000 in taxes from over $1.5 million in income in 2017 and 2018. He had been expected to plead guilty after agreeing with prosecutors, who were planning to recommend two years of probation.

At the time, prosecutors said Hunter Biden remained under investigation. The deal unraveled in July as a federal judge raised concerns about the terms of the agreement.

Just as his appointment as special counsel was announced on Friday, Weiss notified a federal judge in Delaware that plea deal talks in the Hunter Biden case were at an “impasse.”

House Republicans are also mounting their investigation into Hunter Biden’s business dealings. They have been seeking to connect the son’s work to his father and so far have not been able to produce evidence to show any wrongdoing.