The Justice Department appointed former FBI Director, Robert Mueller, Wednesday as a special counsel to oversee the Russia investigation.

The announcement comes after revelations President Trump asked now-fired FBI Director, James Comey, to close the agency's investigation into former National Security Advisor, Michael Flynn.

But just what is special counsel?

Special counsel is a lawyer appointed by the Justice Department to investigate an individual legal case. According to the Code of Federal Regulations (CFR), they are selected outside of the U.S. government, so this usually happens when the regular justice system seems compromised. It should be of public interest to appoint Special Counsel to investigate a specific case.

Special Counsel has "full power and independent authority to exercise all investigative and prosecutorial functions of any United States attorney," according to the CFR.

However, Special Counsel may not be under the supervision of any department but the Attorney General could require explanation from Special Counsel for any step taken.

Who exactly appoints Special Counsel?

The Attorney General is in charge of selecting Special Counsel. However, in the case of the Russia investigation, Attorney General, Jeff Sessions, rescued himself from the Russia probe so the current Deputy Attorney General, Rod Rosenstein stepped in.

Special Counsel was formerly called a Special Prosecutor. Throughout U.S. history, presidents have appointed Special Prosecutors to investigate high-level corruption cases, according to PBS Frontline. However, it wasn't until the Watergate and Nixon administration investigation that the Ethics in Government Act created an Office of Independent Counsel. The 1978 law was designed to allow independent counsel outside the government to lead special investigations in order to reduce potential corruption and use transparency.

Originally, the law was handled by Congress although now, the power to appoint Special Counsel rests solely on the Justice Department.

The law expired in 1999, but not before being used to investigate President Bill Clinton.

Who qualifies as Special Counsel?

The individual selected for Special Counsel should "be a lawyer with a reputation for integrity and impartial decision making, and with appropriate experience to ensure both that the investigation will be conducted ably, expeditiously and thoroughly, and that investigative and prosecutorial decisions will be supported by an informed understanding of the criminal law and Department of Justice policies," according to the CFR.

Those selected for Special Counsel are expected to give the case full priority in their professional lives. The individuals go through a background investigation "and a detailed review of ethics and conflicts of interest issues."

Who can fire Special Counsel?

The Attorney General or in the current case, Deputy Attorney General, has the power to fire Special Counsel.

The President can also fire Special Counsel and this has happened in the past. President Nixon fired special prosecutor, Archibald Cox, after Cox subpoenaed audio tapes of audio tapes of conversations in the White House.

President Ulysses Grant also fired a special prosecutor during the 1875 Whisky Ring Scandal.

What happens after the investigation?

After Special Counsel concludes their work, the Attorney General or Deputy Attorney General decides whether or not there's enough evidence to prosecute.