A report from, where else? The WaPo:
"He secretly guided Washington Post reporter Bob Woodward as he and his colleague Carl Bernstein pursued the story of the 1972 break-in of the Democratic National Committee's headquarters at the Watergate office buildings and later revelations of the Nixon administration's campaign of spying and sabotage against its perceived political enemies."
Six degrees of Hollywood:
"Felt insisted on remaining completely anonymous, or on "deep background." A Post editor dubbed him "Deep Throat," a bit of wordplay based on the title of a pornographic movie of the time. The source's existence, but not his identity, became known in Woodward and Bernstein's 1974 book, "All the President's Men," and in the subsequent movie version, in which actor Hal Holbrook played the charismatic but shadowy source."
Just released this month is Ron Howard’s new film, Frost/Nixon, a re-examination about the only U.S. president to resign from office.
Six degrees of Obama:
"Although Deep Throat was a hero to the counterculture, civil rights advocates and Nixon's opponents, Felt was no friend to the political left.
In 1980, he was convicted of approving illegal "black bag" break-ins against of the families and friends of Weather Underground radicals. He was later pardoned by President Ronald Reagan."
Bill Ayers and wife B. Dohrn were/are the de facto head of the Weather Underground, and well-known associates of President-Elect Obama and his wife.
Our prayers and well wishes go out to Mark Felt's family & friends.