Mark Felt, widely known as Deep Throat, the mysterious FBI source behind the exposure of the Watergate scandal that brought down the then US President Richard Nixon, has died. He was 95.

Felt died yesterday of congestive heart failure at a hospice near his home in California, after several months of failing health. His daughter Joan told the Washington Post that her father "slipped away" in his sleep.

According to the newspaper, he had suffered two strokes in recent years, and his memory of the Watergate era had almost completely vanished because of Alzheimer's disease.

Deep Throat had helped reporters from the 'Washington Post' newspaper uncover abuses of presidential powers in the Nixon White House. The scandal ultimately compelled President Nixon to resign in disgrace in August 1974.

In fact, mystery surrounded the identity of Deep Throat, named after a popular pornographic movie of the time, for decades until Felt admitted being the source in 2005. "I am the guy they used to call Deep Throat," he told popular US magazine Vanity Fair.

Until then, the Washington Post had refused to confirm his identity.

The Woodward and Bernstein book on the Watergate saga, 'All the President's Men', and the subsequent film of the same title made Deep Throat and his "mantra" follow the money legendary in US politics and journalism.

Critics of Felt, including those who went to prison for the Watergate scandal, called him a traitor for betraying the President. Supporters, however, hailed him as a hero for blowing the whistle on a corrupt administration.