One that pops to mind for me is Francis York Morgan, an FBI agent, and the main character of the "horror" game Deadly Premonition.
He's an eccentric, but nice, character who has an imaginary friend he talks to named Zach who helps him solve crimes.
He seemingly only solves serial murders and not assassinating leftist leaders...as far as we know..
Lieutenant Columbo. His befuddled demeanor conceals his keen intellect, and he catches murderers with seemingly-innocent but irritatingly persistent questions. The fact that the crooks he catches are all snooty aristocratic assholes doesn't hurt either.