He was nicknamed "the Boogie-Man," and was known for his enormous size for a hockey player (6'7", 270 lb.) and his reputation as an intimidating enforcer.
I can't imagine what could have caused this. I sure hope it had nothing to do with head injuries or anything of that sort.
At his size I would suspect a heart attack.
http://1500espn.com/blogs/Deaths_great_mystery_hits_hard_again