Short answers, pulled from the story.
Mark Felt served as the anonymous informant known as Deep Throat during the Watergate investigation. He was a former FBI Associate Director who provided critical information to Washington Post reporters Carl Bernstein and Bob Woodward.
Vanity Fair reported on the 31st of May 2005 that Mark Felt claimed to be the source. The Washington Post confirmed his identity later that same day with a joint statement from Woodward, Bernstein, and Ben Bradlee.
Woodward met Mark Freet at an underground garage located at 1401 Wilson Boulevard just over the Key Bridge in Rosslyn. They conducted six meetings between October 1972 and November 1973 often at 2:00 a.m. on the bottom level of this facility.
The identity of Deep Throat remained unconfirmed for over thirty years following the initial burglary on the 17th of June 1972. Public curiosity persisted until Mark Felt revealed himself in 2005 after decades of denial.
Felt leaked information because he believed he was protecting the FBI from political manipulation by the White House. He felt angry and disgusted when L. Patrick Gray replaced J. Edgar Hoover as Director and sought to push information out to the public through Woodward.