Actor/bodybuilder Steve Reeves was the model for Joe Meach, the janitor who received the powers of The Legion of Super-Heroes after being struck by lightning.
The Composite Superman appeared in World's Finest 142. Just pulled it out of my collection to check the facts.
He was a guy named Joe Meach, basically a nobody with a grudge against anyone successful (especially Superman and Batman). He was in a museum standing in front of a bunch of statuettes of the Legion of Super-Heroes, when lightning struck them and some sort of odd radiation coming from the statuettes gave him the powers of the entire Legion (including Superboy and Monel.)
A lot of people thought he was a lame character but I thought the concept was rather cool myself.