Now identified around the world, Mark Felt is the greatest whistle-blower of our time.
He was a former number two at the FBI, who with Washington Post reporters Woodward and Bernstein, changed American political history.
But there have been other whistle-blower cases that altered the political landscape.
In 1971, with Vietnam raging, military analyst Daniel Ellsberg leaked classified documents to the New York Times. "The Pentagon Papers," as they were called, revealed that nearly everyone in the Pentagon and state department knew that the U.S. had no realistic chance of winning the war.
The story fueled anti-war protests and added to the public pressure that pushed the Nixon administration towards peace talks. As for Ellsberg, because of administration misconduct against him, charges of theft and espionage were dropped.
America's most famous corporate whistle-blower was a tobacco executive named Jeffrey Wigand.
Thanks to his leaks first to CBS’s "60 Minutes," the CEO’s of Big Tobacco were hauled before Congress, their companies were successfully sued by the states, and the government began regulating tobacco advertising. Hollywood memorialized Wigand as a hero in the film, "The Insider."
In 1997, Jennifer Long blew the whistle on widespread misconduct at the Internal Revenue Service. The IRS then tried to fire Long, but Congress stopped the retribution and passed laws giving taxpayers new powers.
Three years ago, Time Magazine honored as its “Person’s of the Year,” whistle-blowers Cynthia Cooper of Worldcom, Sherron Watkins of Enron, and Colleen Rowley of the FBI. Rowley, an FBI staff attorney, caused a sensation with an open memo about how the bureau had brushed off her concerns over Zacharias Moussaoui, who was later indicted as a 9/11 conspirator.
Some government insiders first tell their stories in a book. Former White House counter terrorism adviser Richard Clarke testified that before 9/11, al-Qaeda was not an administration priority. And in Congressional hearings, he apologized to the 9/11 families.
The most recent high profile whistle-blower case came last year: Army specialist Joseph Darby leaked thousands of photos showing abuse at Abu Garib prison in Iraq.
In recent years, whistle-blowers have had a dramatic impact. But what sets Mark Felt apart is that his efforts helped bring down a sitting president. Even more remarkable, say historians, is that Felt was able to keep his role a secret for more than 30 years.