Arnold Schwarzenegger is simply the best bodybuilder of all time! He completely DOMINATED his peers, winning the Mr. Olympia title an unprecedented (then) six consecutive times! He retired and came back in 1980 to win it again (albeit in a controversial way).
Schwarzenegger then went on to become one of the most successful Hollywood action heroes, elevating the visibility of the sport of bodybuilding, benefiting all the champions that have followed him.
Of course, never satisfied, Arnold then entered politics, and the rest, as they say, is history. Not sure where he can go from here, but I'm sure he's already got it all planned out!
Arnold not only was the best of his time, but he has done more for the sport of bodybuilding than any other champion. For that, he holds the esteemed #1 position on my list.
You can find out more about Arnold here.