Conversation so far:
What was the basic plot of Trapped In The Closet?
the president of Scientology determines that, because his reading is so high, Stan must be a reincarnation of L.
Ron Hubbard.
What happens after that?
Later that night, a large group of Scientologists, including John Travolta, gather outside the Marsh house to celebrate.
Is Tom Cruise a character as well?
Randy sends Stan to his room, where he finds Tom Cruise waiting.
What does Tom Cruise want with Stan?
Cruise, believing that Stan is genuinely Hubbard's reincarnation, asks him whether he has enjoyed his acting.
What does Stan tell him?
"Hubbard" replies that his acting is okay but not as good as others' such as Leonardo DiCaprio.
What other famous actors are depicted?
He refuses to come out, despite the entreaties of Randy, Nicole Kidman, the police, Travolta and R.
Kelly.

Question: Why is R Kelly there?
Self-contained rewrite: Why is R Kelly in the South Park episode Trapped in the Closet?