Fallout Boy was Radioactive Man's sidekick from The Simpsons and the short-lived RM comic book. He wore a green costume and had basically no super powers, other than the ability to fly. His secret identity, the name of which escapes me, lived with RM batman style. He was once played by Milhouse in an episode of the Simpsons.

"Billowing backpacks, Radioactive Man: it's the worst villain of them all -- the Scoutmaster! --Fallout Boy