People have been debating whether Mark "Deep Throat" Felt was a good guy or a bad guy, and these debates often seem to be conducted on the assumption that he had to have been one or the other.
I don't think many public figures — especially in government — can be fit wholly into one of those two classifications, and I see no reason to expect that Mr. Felt can be so tidily rated. His motives in leaking to Bob Woodward were probably some mixture of wanting to protect the FBI from abuse by the Nixon administration and wanting to advance his personal agenda. In the grand scheme of things, I suspect he was less important to the toppling of a president than he was to the career advancement of Woodward and Bernstein. I don't think what he did was dishonorable or illegal — that's the spin of those who cast their lot with Richard M. Nixon — and to the extent he did it to expose corruption, I guess he's a hero.
But only for that one series of actions. He wasn't a hero for what he did soon after. This article tells all about that.