The man once known to the world only as "Deep Throat" has died at the age of 95.

W. Mark Felt, the one-time anonymous source behind some of the key news stories that forced late president Richard Nixon to resign in the wake of the Watergate scandal, passed away in Santa Rosa, Calif. He had been suffering from congestive heart failure for several months, a family friend said.

Felt, a top FBI commander in the 1970s, provided Washington Post reporters Carl Bernstein and Bob Woodward some of their most significant leads in a series of stories following what appeared to be a low-level break-in of the Democratic National Committee's headquarters at the Watergate Hotel.

With Felt's help, the reporters were able to trace the origins of the 1972 crime to the Republican White House and Nixon.

Allan Lichtman, a political historian at Washington's American University, said Felt played an indisputably important role in bringing a difficult truth forward to the American people.

Without Felt's efforts, "it's quite possible that the worst scandal in the history of the country may never have been fully probed, may never have been fully understood and Richard Nixon may have gotten away with crimes of Watergate and even served a full second term," Lichtman told CTV Newsnet in a phone interview from Washington.

"Of course, we don't know that for sure -- perhaps probes by the United States' Senate, the impeachment inquiry by the House, might have revealed the truths of Watergate, but certainly Mark Felt was a great catalyst in setting in motion the process that led to Richard Nixon becoming, still today, the only American president to resign the office."

But Felt had one condition in exchange for his tips, which were often given to Woodward in a shadowy Washington garage. He wanted to keep his identity a secret until his death. Woodward agreed and the reporters kept the mystery alive for three decades. In May 2005, however, Felt decided to reveal the secret himself.

"I'm the guy they used to call Deep Throat," Felt told Vanity Fair before letting the rest of the media in his secret.

"People will debate for a long time whether I did the right thing by helping Woodward," Felt wrote in his 2006 memoir, "A G-Man's Life: The FBI, 'Deep Throat' and the Struggle for Honor in Washington."

"The bottom line is that we did get the whole truth out, and isn't that what the FBI is supposed to do?"

Many Americans considered Felt a hero for exposing the nefarious political activities of Nixon and some of his White House staff, even if he didn't come forward for decades. But critics said he was motivated more by his personal bitterness at being passed over for a promotion than by patriotism.

"We had no idea of his motivations, and even now some of his motivations are unclear," Bernstein said.

Felt denied he was motivated by anger.

"It is true that I would have welcomed an appointment as FBI director when Hoover died. It is not true that I was jealous (of the successful candidate)," he wrote.

Solon Simmons, an associate professor at George Mason University, said he thought Felt may have been motivated by a desire to show the public what was going on inside the highest political office in the country.

"There's a sense that...he felt like Nixon was engaged in a pattern of dirty tricks that needed to be exposed," Simmons told CTV Newsnet in a phone interview from Washington.

The wiretapping and other tactics used by the Nixon administration were ugly truths that needed to be told, he said.

"I think he did it because it needed to be done, but is shows the tensions between security and civil liberties that existed at the time and still exist today."

Unable to name their source, Woodward and Bernstein's editor dubbed him "Deep Throat" after the name of a pornographic movie that was in theatres at the time. The mysterious figure played a central role in what would become one of the biggest scandals in U.S. history and gained international notoriety after Woodward and Bernstein's book on the affair was turned into a movie.

Hal Holbrook played Felt in "All the President's Men," portraying him as a gravelly-voiced, chain-smoking source who gave clues to Woodward, but was often not explicit. Instead, according to the movie, he offered tips. Felt's method of providing clues gave the movie one of Hollywood's most memorable lines: "follow the money," he told Woodward, as he puffed away on his cigarette.

"From the start, it was clear that senior (Nixon) administration officials were up to their necks in this mess, and that they would stop at nothing to sabotage our investigation," Felt wrote in his memoir.

Although Woodward and Bernstein didn't reveal their source (until after Felt's confirmation), Nixon and his staff had their suspicions about Woodward and Bernstein's source. It turned out, however, the White House was afraid to reveal the secret without jeopardizing their own secrets.

Is it "somebody in the FBI?" Nixon is heard asking a member of his administration on the Watergate tapes.

The response: "Yes, sir. Mark Felt ... If we move on him, he'll go out and unload everything. He knows everything that's to be known in the FBI."

Felt is survived by two children and four grandchildren.