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Mel joined the cast of The Krusty the Clown Show to replace Sideshow Bob in April 1990, who was sent to prison for attempting to frame Krusty for armed robbery the previous month. It seems that Krusty unceremoniously replaced Bob with someone even stranger-looking than he was.
Sideshow Mel uses a slide whistle to communicate on camera. When not in character, Mel speaks in a grandiose British/Shakespearean accent and owns poodles. His main accomplishment so far has been successfully removing Waylon Smithers, Jr. from suspicion of having shot Mr. Burns. Off-screen, Mel is generally very eloquent, educated, poetic and intelligent, with a beautiful singing voice-it is implied that, as with Sideshow Bob before him, his true talents are wasted on Krusty's show. When Lisa Simpson won the "Entertainer of the Year Award"; it was revealed that Melvin also won the award previously for his portrayal of Biff in Death of a Salesman, but his desire to keep his stardom eventually led him to become the sidekick he is today. He was once forced to conduct an orchestra of kazoo-playing monkeys. When he pleaded with Krusty to not force him to do it, Krusty simply shouted at him to "shut up and conduct!"
 Religion and Education
Little is known about Mel. He is a Cornell University graduate and an Atheist (though he is occasionally seen at the Presbylutheran church). It is also shown that Mel could be a recovering alcoholic as he had attended several Alcoholic Anonymous meetings.
Aside from the bone, Mel has curly green hair in a sort of beehive-like style similar to Marge's only shorter and rounded at the top,his hair also appears to be "fashioned/poised/set" in an upward position because it seems to sit atop his head showing that he has no sideburns or even a hair "tail". Mel perpetually wears a bone in his hair which may or may not be permanently affixed. He once warned Lisa Simpson not to use a bone to try and get gum out of her hair, as he did and it became permanently stuck there. However, he was once seen removing the bone and using it as a weapon during a duel. When Springfield was trapped under a dome by the EPA, he was also seen removing the bone and whacking it at the dome. Bart also took the bone out of his hair pranking Martin Prince, Jr.. He indicated that he could feel meteorological conditions in the bone, such as incoming storms. Before he got his bone, Mel was famous in both London and Hollywood and was able to comb his hair.
Bart Simpson found out that Mel is lactose-intolerant. Krusty once poured liquid nitrogen down Mel's pants and cracked his buttocks with a hammer.
He may be married to or living with a woman named Barbara with whom he wished to purchase a house from Marge Simpson. Mel once complained that Barbara no longer pleasured him with the French Arts. Mel also has a son (that looks exactly like him but has no bone in his hair) who's name was/is never mentioned directly or indirectly. Mel's last name of Van Horne may suggest his family is of Dutch/Afrikaner origin.
Krusty reveals to Mel that he has been secretly dating Mel's wife, and that he wants to dump her after 11 years since the thrill is gone.
 Other jobs
After Krusty's show was cancelled following the rise of Gabbo, Mel worked at a taco stand where he initially refused Krusty's pleas to return to his show.
 The Simpsons: Tapped Out