I'm very sad to hear about this. When I first started watching wrestling as a kid, Heenan was one of the personalities who got me hooked on it. He was managing Nick Bockwinkel, and played the role of the dishonest cowardly heel manager better than anyone else I can remember. I didn't hate him like other fans did, just because he was so entertaining.
Obviously best known as a manager and an announcer, but his work as a wrestler was very underrated on the rare occasions he laced up the boots. He could take bumps better than most full-time wrestlers.
RIP to the greatest manager of all-time.