Fallout Boy

Fallout Boy is the sidekick in the comic book series Radioactive Man. In the series, Fallout Boy first appeared in a 1950s Radioactive Man film serial shown at a comic book convention in the episode "Three Men and a Comic Book", and it was implied that the actor who played Fallout Boy might have been gay. However, unlike many Simpsons characters, he has only made a handful of appearances since.

Creation
While Radioactive Man is a broad parody of many superheroes, most obviously containing elements of Batman and Superman (and the comic incorporates an origin story similar to Marvel's The Hulk), among others, Fallout Boy is mainly a parody of Robin (with his costume, references as being the 'young ward' of Radioactive Man, and his younger age and sidekick status) with elements of Spider-Man (his fictional comic book origin, for example).

Catchphrase
His catchphrase: "Jiminy jillickers!"

Real Life
Additionally, Fallout Boy also appears in a real-life comic book titled Radioactive Man, published by Bongo Comics (a comic created in part by Matt Groening, the creator of The Simpsons). In these comic books, Fallout Boy's real name is Rod Runtledge, he has a brother named Dodd Runtledge, and they live in Zenith City. Rod is a high school nerd living with his aunt, Aunt June, an obvious reference to Spider-Man's alter ego, Peter Parker, who lives with his Aunt May.

Orgin
Fallout Boy was an average bookworm, until one day he met billionaire playboy Claude Kane (Radioactive Man) at a radioactivity convention. A tall piece of machinery fell towards them. Claude grabbed Rod and jumped over the rail, Claude holding onto the machine. The machine came to life, and as the ray passed through Claude, it hit Rod. Rod received a pint-sized version of RM's powers, and became Fallout Boy.

Film
Milhouse was chosen to play Fallout Boy in the Radioactive Man movie. Emocore band Fall Out Boy is named after this character.