Who played Watergate cover-up informant 'Deep Throat' in the film "All the President's Men"?

I should have worded that differently. He & his late wife, Dixie Carter.

I saw Mr.Holbrook in a Tennessee Wal-Mart in the 90s! He was pushing a cart shopping like everyone else.He & his wife,Dixie Carter have a home here in Tennessee only a few miles from us.