Leon Kompowsky

Leon Kompowsky is a former mental patient. Hospital staff initially believed him to be under a delusion that he was, referring to him as the "big white guy who thinks he's the little black guy".

Biography
Leon Kompowsky worked as a bricklayer in his early life and was angry about himself until he started impersonating the voice of Michael Jackson, which gained him respect. He was placed in New Bedlam Insane Asylum where he later met Homer, who got hospitalized for wearing a pink shirt to work. Leon impersonated Michael Jackson though Homer had no clue who Michael Jackson was. After getting released, Homer invited him to come visit his home (Kompowsky was in the hospital voluntarily) and Bart, thinking Kompowsky was the real Michael Jackson, told everyone. The entire town showed up to see Michael Jackson, only to learn it was fake. Bart became hated in the town, and Lisa hated him too for forgetting about her birthday. Kompowsky decided to set things right and helped Bart write a special birthday song for Lisa. In the end, his work was done, so Kompowsky dropped the Jackson charade and started talking in his normal voice, citing his reasons for doing the voice was a result of anger and he felt respected when he did the Jackson impersonation, he then cited his work at the Simpson home was done prior to leaving.

He also took part in a record attempt for the world's tallest human pyramid.

When Lisa decided to write a new town anthem, Bart mentioned that he previously wrote a song with Kompowsky, then questioned why Homer and Marge let them hang around together in a room. Homer responded that it was a simpler time.

Non-canon
Kompowsky once dressed up as Fallout Boy and accompanied Homer while the latter thought he was.

In the February picture of "The Simpsons 2009 Calendar", he is a part of an angry mob.

On Lisa's 14th birthday, Leon and Bart sang her a new version of "Happy Birthday, Lisa".

Trivia

 * Leon Kompowsky was voiced by Michael Jackson (who, for contractual reasons, was credited as "John Jay Smith") but his singing was done by Jackson impersonator Kipp Lennon.
 * Kompowsky was set to later return, except this time as Prince, but the idea fell through.