Mark Felt, the former No. 2 man in the FBI, sat on the world's most-notorious secret for more than 30 years -- he was Deep Throat.
He brought down the Nixon presidency by leaking details of the Watergate case to two reporters for The Washington Post.
"Dad is so persuasive that when he said that he wasn't, I believed him," his daughter Joan Felt said. "We had people calling. The media calling every year on the anniversary, and he always denied that he was and I went along with it."
Now Felt is telling his story for the first time in a new book, co-written with John O'Connor, called "A G-Man's Life." Joan Felt said that now the world would really know how the most-legendary anonymous source really viewed Watergate.
It was a mystery to Joan Felt until a woman her father had dated after his wife committed suicide in 1984 revealed his past. She said she then pressed her father to tell her the truth.
"I said, 'Dad, if this is the truth, I think you should tell the world,'" said Joan Felt, who never knew the pressure her father faced while she was a child.
O'Connor, who wrote the story for Vanity Fair magazine that outlined Mark Felt's role as Deep Throat, said that the book was an attempt to answer long-lingering questions and give Felt an opportunity to bask in Deep Throat's glory.
"This was the most daring of all his daredeviltry," O'Connor said. "He was the only person in a position to know the entire conspiracy and yet not be part of it, so he either was going to be complicit with it and violate every standard of honor he had or he was going to do something about it."
O'Connor dismissed the notion that Felt acted out of a personal vendetta against the Nixon White House and that he was trying to get a promotion.
"He had helped out President Nixon when he needed it on the Wallace shooting," O'Connor said. "He made Pat Gray look like a million dollars. He's made them look good on everything else."
The problem, O'Connor said, was that Felt had too much love and respect for the FBI and did not want to see it tainted and used.
"He didn't want the American people to be lied to, either," Joan Felt said.
Deep Throat was immortalized in the movie "All the President's Men" based on the book written by Washington Post reporters Bob Woodward and Carl Bernstein about uncovering the Watergate scandal. The way Hal Holbrook portrays him in the film is far different from the man Joan Felt knows.
"I have to say John nailed it," she said of the new book. "It's such an accurate representation of him."
With the weight of the secret off his shoulders, her father is "having so much fun now," Joan Felt said.
"He's having the time of his life," she said.