Michael Jackson in Men in Black II (2002)
Director: Barry Sonnenfeld
Jackson, apparently, loved the first Men in Black so much that he personally called up Will Smith and said if there was ever a sequel, he wanted in. So, naturally, the King of Pop was in MIB 2.
And what people don't seem to realize about the singer is he actually had a terrific sense of humor about himself. Hell, he played an alien. With no stage make up. Just his face.