We have just lost a great man. He was W. Mark Felt, who headed the FBI's Watergate investigation, cleverly fighting White House obstruction of it by becoming Bob Woodward's legendary ubersource. But we would be remiss if we limited our historical assessment to this one courageous role.

Hard working, intelligent and handsome, Felt eschewed pursuit of wealth for a career protecting American citizens, confronting wisely every modern national security issue.

He hunted Nazis during World War II and searched for communist infiltrators afterward. During the Vietnam War era, he protected anti-war demonstrators in spite of White House efforts to punish them. He relentlessly, and with scrupulous legality, searched for foreign-inspired terrorists, in spite of opposition from well-meaning civil libertarians unaware of their destructive agenda.

A conservative Democrat philosophically in tune with the Nixon administration, he opposed the "switch-blade mentality" of politically abusive White House aides, refusing, for example, to whitewash the infamous Dita Beard/ITT corruption case. He leaked to Woodward that Arthur Bremer, the would-be assassin of George Wallace, was a crazed loner, clearing both Democrats and Republicans of countervailing charges of responsibility.

Following closely on the death of J. Edgar Hoover and the Wallace shooting, the Watergate investigation challenged the FBI's integrity and political neutrality.

Only when it appeared that the coverup would be successful did Mark Felt begin his close, courageous cooperation with Woodward -- to explain the larger conspiracy and to impart confidence to Washington Post editors intimidated by White House bullying.

A fierce FBI loyalist, he sought to curb its excesses, especially those of his amoral b?e noire, Associate Director William Sullivan. He defended the wiretapping of Martin Luther King Jr. (President John F. Kennedy worried that King's continued association with known communists would hurt the burgeoning civil rights movement), but was outraged at Sullivan's exploitation of the seamier aspects of King's private conduct.

As the threat of foreign-inspired communism waned, so did the Bureau's use of wiretaps and warrantless "black bag jobs."

But after modern terrorism reared its ugly head at the 1972 Munich Olympics, and he learned that PLO assassins and Weather Underground bombers were threatening New York City, he resumed them.

Ironically, Felt's decision to use breakins to fight terrorism -- in cooperation with the White House -- came at the same time he began meeting with Woodward to expose the illegal political break-ins of the same White House.

He was indicted in 1978 for these warrantless entries on a bum rap, as Carter's prosecutors sought a scalp in the Watergate reformist backlash. But he stoically refused to play the Deep Throat card that would have freed him.

He listened impassively as disgraced former President Richard M. Nixon testified to the clear presidential delegation of authority to the FBI for these legitimate national security actions. This testimony should have automatically acquitted Felt, but the neophyte judge all but ordered the jury to find him guilty.

He watched his intelligent and beautiful, but highly nervous, wife Audrey begin her deterioration after listening to the righteous prosecutor portraying her husband as a common criminal.

President Ronald Reagan pardoned Felt after his conviction, but that was no solace to Audrey, who eventually took her life with his service revolver.

Felt's government had criminalized him and taken his wife, but he resisted bitterness. He read, with ironic, witty detachment, scathing editorials denouncing him in the Washington Post, on which he had bestowed Pulitzer prizes and worldwide recognition as a great newspaper.

He warned anyone who would listen that Congress' crippling of intelligence programs would inevitably lead to terrorist disaster, a prophecy that came all too true on Sept. 11, 2001.

He continued to admire Bob Woodward, even though to sell books Woodward, to Felt's discomfort, told the world about "Deep Throat." Two months after the publication of "All the President's Men," Nixon's FBI, suspecting Felt of being Deep Throat, began a criminal investigation of him.

Felt knew that extraordinary circumstances had compelled him to meet Woodward in that Arlington garage and helped save our democracy from kingly corruption. But he so believed in the FBI's strong code of conduct, one he had enforced ruthlessly on subordinates, that he did not believe that America's honest and upright citizenry would approve of his actions.

But approve they did in 2005, something perhaps not likely in 1975. What he had not realized was that his daring actions during that Watergate investigation had permanently seared into the hearts and minds of young Mark Felts the value of truth over power.

Gratified by America's embrace of his incorruptibility, Felt was bothered not a whit either by criticisms from stunningly clueless FBI retirees or denunciations of Hoover's FBI by a surprisingly ignorant Woodward.

Like a grownup Holden Caufield, laconic Mark Felt preferred saving acts over empty words, which, unfortunately and ironically, are all we have to offer now on his behalf to the American public: Thank you for appreciating integrity and for making the last three years of his 95-year life so joyously happy.

John O'Connor, a San Francisco lawyer and former federal prosecutor, was Mark Felt's lawyer and co-author with Felt of "A G-Man's Life."