And Deep Throat Is...

W. Mark Felt? Or so he claims... Vanity Fair claims he admitted that he is the famous Watergate whistleblower.

Here a resume (of sorts) for W. Mark Felt

Ronald Reagan gave him a pardon for authorizing FBI agents to break into Vietnam protestors' offices without warrants.

Read Reagan's statement on the pardon

Here is some old Deep Throat speculation that includes W. Mark Felt:

Slate 2002

Answers.com

Washington Post