In Hollywood, they say you're not famous until you've done a guest spot on "The Simpsons," which means that Michael Jackson's fame was confirmed in September of 1991 when he provided a guest voice on the third season premiere "Stark Raving Dad." In the episode (considered a classic amongst aficionados), Homer gets sent to a mental institution and meets a man named Leon Kompowski, a bald oaf who thinks he is actually Michael Jackson. Kompowski's voice? Jackson himself. At the time of the episode's airing, a contractual conflict didn't allow the show's creators to confirm that Jackson was on the show or even allow for him to be credited, which is why the voice of Leon Kompowski is in the credits as "John Jay Smith." Subsequent interviews and DVD commentaries have confirmed that it was in fact Jackson playing the role. Show creator Matt Groening later established a that all subsequent guest stars would have to be credited by their actual names.
Interestingly, Jackson doesn't do any of his own singing on the show (the difference in the sound of his voice led to a lot of people thinking it wasn't really Jackson, furthering the confusion over his casting). Because his record contract wouldn't allow him to sing for any company but them, both his version of "Billie Jean" and the birthday song he sings to Lisa at the end are sung by frequent "Simpsons" collaborator Kipp Lennon.
Jackson was a huge fan of the show — he even wrote probably the most famous musical hit from the show, "Do the Bartman." That song appeared on the album The Simpsons Sing the Blues, and Jackson apparently approached "Simpsons" creator Matt Groening about writing a song for Bart. Speaking at an animation conference in 1998, Groening admitted that Jackson had written the song and that he had always been amazed that fact hadn't ever gotten out.