(Gibson) It was not Michael Jackson's voice that sang "Happy Birthday Lisa" on The Simpsons TV show in 1991. In the episode, "Stark Raving Dad," Jackson voiced a character who was a mental patient, but was not allowed to sing his own song.
According to NME.com, Jackson had written the song especially for the show, but was blocked by his record company, Sony, from actually singing it.
The singing voice belonged to Jackson impersonator Kipp Lennon, who also voiced Jackson in the TV series The Jacksons: An American Dream. more on this story