At the time of the making of this film, Deep Throat's identity was still unknown to the public. In 2005, he was revealed to be William Mark Felt Sr. (1913-2008), who at the time was Associate Director of the FBI, the second-highest position in the organisation. Bob Woodward had met Felt a few years before Watergate. According to Woodward, while he was still in the Navy he had been sent to deliver some papers to the White House. While waiting, he struck up a conversation with an older gentleman who was also waiting. That man was Mark Felt. Woodward, who had not yet decided to take up journalism, asked Felt for some career advice and the two men became friendly. Later, when Woodward was working at the Washington Post, he would occasionally use Felt as a deep background source on stories. At this point, Woodward openly referred to Felt in the the newsroom as "My friend in the FBI." When Woodward and Bernstein began investigating Watergate, Woodward once again turned to Felt for inside information. To keep Felt's identity secret, Post editor Ben Bradlee began referring to him as "Deep Throat" a mashup of the journalistic term "deep background" and a reference to the then popular pornographic film "Deep Throat".
In his book about Felt, "The Secret Man", and in related interviews, Woodward has described Felt's motivations for acting as their source, as being entirely patriotic. Felt was concerned about the abuses of Power that Nixon was engaged in. However, Felt may have had less charitable and more personal motives as well. Felt was a protege of FBI director J Edgar Hoover. While he was alive, Hoover maintained an iron grip on control of the bureau and often had his agents engage in legally questionable tactics in pursuit of people who Hoover felt threatened American society, including political dissidents and civil rights leaders. When Hoover died, most of his subordinates at the FBI believed that he would be replaced from inside the bureau, by someone who would continue his legacy. Felt himself even apparently entertained the idea that he might be named director. However, Nixon had other ideas. He, like a number of Presidents before him, disliked the autonomy which the FBI had enjoyed under Hoover. With Hoover dead, Nixon saw this as his chance to rein in the Bureau. He appointed Deputy Attorney General L Patrick Gray to head the bureau. Felt, like many Hoover loyalists, resented this as an attempt by Nixon to control the Bureau and trample on the autonomy which they had traditionally enjoyed.
Ironically Felt himself would later be convicted of illegal break ins and wiretapping which he had authorized against radical left wing groups. One of the witnesses called by his defence team was former president Richard Nixon who also contributed to Felt's defence fund and actually sent him congratulatory bottles of champagne when Ronald Regan later pardoned him.