Brimmy (sometimes erroneously Brad Dixon or Blue Cap) is a longtime background character in South Park. His popularity has surged in recent years with fans, with a growing number of deviations and even a few fanfiction appearances by the character.
Please visit his article on the South Park Archives for more information.
Brimmy wears clothes that are very similar to Craig's usual garb, he wears grey trousers, a blue coat and a blue cap with a yellow brim. He appears in almost every episode up until "Fourth Grade". Since then, his background appearances have slightly decreased, but he is still a frequent background character.
Despite having been the Boys' classmate since third grade, he's never spoken, although he makes groans and noises in "Conjoined Fetus Lady" and "Quest for Ratings". He was once jokingly said to be unable to enter the classroom due to the fact he was seen entering the classroom in "Fourth Grade" but is not seen sitting in a seat.
The handle "Brimmy" was first used in 2000 by Fruitbowl in his column "The Cast of Kids", a notable resource that was even used and assisted in by Willie Westwood, who runs the South Park Scriptorium website and moderates at the official South Park Studios message board. The character generally went nameless for several years after the site was taken down, however after the airing of "The Ring" in 2009 many claimed unseen character Brad Dixon was Brimmy. In an attempt to stop this, the name Blue Cap from Fruitbowl's site was used for Brimmy erroneously, but both names have since fallen into common use by South Park fans.