What's with the steroids talk?? Have you seen Big Boss Man??? He was hardly buff at all. Now if you said "painkillers" that is something different. A few wrestlers (Brian Pillman, I think Rick Rude) died due to overuse of painkillers. He did have a bad knee so maybe it could have been that? Could be a heart attack as well.
I enjoyed Bossman's first WWF run when he had matches against Hulk Hogan, Mountie. How about his hilarious feud with the Big Show that culminated in that hilarious funeral scene! I was dying of laughter when Bossman drove away dragging the casket with Big Show on top of the casket.
His WCW run on the other hand was awful.. the Guardian Angel??? Big Bubba Rogers??!! eh...
42 is way too young.
update: It was a heart attack that did him in. (from pwinsider.com)