The Simpsons: 15 Celebrity Appearances You Might Have Missed

14. Michael Jackson

Episode: Stark Raving Dad (Season 3) This is probably one of the most bizarre guest appearances in Simpsons history, so it's no surprise that Michael Jackson is involved. At least, partially. In this classic episode, the late-singer was indeed the voice behind Leon Kompowsky, the mental patient who believed he was the real MJ, despite the singer being omitted from the credits. Instead, he was credited under the name John Jay Smith, but he was not the only voice actor involved with his character. Jackson was blocked by his Sony record label from performing his specially-written song, 'Happy Birthday Lisa' so The King Of Pop selected impersonator Kipp Lennon to sing instead, while Hank Azaria recorded Kompowsky's normal voice at the end of the episode after admitting that he knew he wasn't really Michael Jackson at all.