William Mark Felt Sr. was an American law enforcement officer who worked for the Federal Bureau of Investigation (FBI) from 1942 to 1973 and was known for his role in the Watergate scandal. Felt was an FBI special agent who eventually rose to the position of Deputy Director, the Bureau's second-highest-ranking post. Felt worked in several FBI field offices prior to his promotion to the Bureau's headquarters. In 1980, he was convicted of having violated the civil rights of people thought to be associated with members of the Weather Underground, by ordering FBI agents to break into their homes and search the premises as part of an attempt to prevent bombings. He was ordered to pay a fine, but was pardoned by President Ronald Reagan during his appeal.

The Deputy Director of the Federal Bureau of Investigation is a senior United States government position in the Federal Bureau of Investigation. The office is second in command to the Director of the Federal Bureau of Investigation. If the director is absent or the position is vacant, the deputy director automatically takes on the additional title and role of acting director. The office is also the highest position attainable within the FBI without being appointed by the President of the United States. Responsibilities as deputy director include assisting the director and leading prominent investigations. All other FBI executives and special agents in charge report to the director through the deputy director. From 1978 to 1987, the position of deputy director was not filled due to William Hedgcock Webster's decision to divide the deputy's responsibility between three positions.