Whether or not Jackson actually voiced the part of Homer's mental institution mate Leon Kompowsky went unconfirmed for years. It even made it into my book Truth and Rumors: The Reality Behind TV's Most Famous Myths.
"Yes, that was Michael Jackson,” Simpsons’ creator Matt Groening confirmed when I asked him directly at the January, 2007, TV critics press tour in Los Angeles.
For years Groening and other denied it. In fact, executive producer James L. Brooks still refused to confirm it when I approached him at the same event as Groening. “I think we made a promise,” said Brooks.
Groening later explained that keeping Jackson’s contribution a secret, “was a contractual thing, and I never signed the contract.” In the third-season Simpsons episode, Stark Raving Dad, which first aired in September of 1991, a tubby, bald, lumpy looking character named Leon Kompowsky meets Homer in a mental institution and claims to be pop star Michael Jackson. The character sure sounds like Jackson, except at the end of the episode, when he reverts to a gruff voice more in tune with his character, which supposed to be a New Jersey bricklayer.
Kompowsky befriends Bart and helps him write a sweet little song to his sister called Happy Birthday Lisa. The voice credit at the end of the episode read John Jay Smith. Go ahead, look for him on the Internet Movie Database (IMDb) -- it takes you straight to the Michael Jackson page.
Despite denials from Fox and Simpsons publicists, there was immediate speculation that Jackson, always a big cartoon fan, had recorded the voice for the character. The so-called King Of Pop had already earned a reputation as eccentric, with tales of anti-gravity chambers and Elephant Man bone collections already making the rounds. There was, however, no whiff of child molestation accusations at the time this episode first aired.
The Simpsons had already, at this early stage, let one big name guest voice get away with hiding behind a pseudonym. In Season Two, Dustin Hoffman played Lisa’s substitute teacher Mr. Bergstrom. He was simply credited at the end as “Sam Etic” (Semitic, get it?). Word that it really was Hoffman quickly leaked out — if it wasn’t already obvious in the scene where Bergstrom says, “Mrs. Krabappel, you’re trying to seduce me” (a reference to Hoffman’s breakout film, The Graduate).
In Planet Simpson: How A Cartoon Masterpiece Documented An Era And Defined A Generation, author Chris Turner asserts that it was indeed Jackson’s voice on the episode — although only in the speaking parts, not the singing voice used on Happy Birthday Lisa (credited to voice over actor and Jackson sound-a-like Kip Lennon).
That is how Yeardley Smith remembers it. Smith, the voice of Lisa Simpson,
recorded her lines at the same time as Jackson. “That was an extraordinary day,” she recalls. She Remembers Jackson as “very quiet and he was really into being there.”
“It’s kind of dazzling for us when you have a huge star in our environment,” says Smith, who was equally star-struck when Elizabeth Taylor came in to utter baby sister Maggie’s only words: “Dad-dee.” Recalls Smith, “she brought her little dog with her.”
The irony in all of this is that Jackson never appeared more flesh and blood, more human, than as cartoon character Kompowsky. The episode remains one of the most affecting Simpsons’ episodes ever.