Radiohead appears in "Scott Tenorman Must Die". In the show, the band seems to be touched by Eric Cartman's letter, and goes to South Park to comfort Scott Tenorman, but after seeing him cry, they insult him and leave.
Background
Behind the Scenes of "Scott Tenorman Must Die"
In real life, Radiohead came up with the idea of Scott eating his parents in chili. This is confirmed in commentary minis with Matt Stone and Trey Parker.
Appearance
They all wear clothing of varying appearance, however their basic outfit is the same: pants, a shirt or coat, and an undershirt, however, two members of the band do not wear a shirt or coat.
Personality
They seem to be caring, leaving their work just to visit Scott Tenorman, due to a letter Cartman sent, that claimed he had "ass cancer". However, this is later revoked when they see Scott crying. This leads to them insulting him and leaving.