A military analyst, he passed the Pentagon Papers -- a secret Defense Department study of U.S. involvement in Vietnam -- on to The New York Times and other newspapers in 1971.
An associate director at the FBI, he was Deep Throat, the source who gave information about Watergate to The Washington Post in the 1970s. Felt, seen in this photo with his daughter Joan, unmasked himself in 2005.
He was an Israeli nuclear technician in 1986 when he revealed Israel's nuclear weapons program. He served 18 years in prison.
Beginning in 1992, the FBI agent exposed shoddy work and inaccurate testimony from the bureau's crime lab.
A Brown & Williamson tobacco executive, he cooperated with CBS television news magazine "60 Minutes" and the Food and Drug Administration in the 1990s in exposing cigarette manufacturers' practices.
The U.S. Army private gave a trove of classified military and diplomatic material to WikiLeaks. His court-martial is underway at Fort Meade, Maryland.