Robert Guillaume -- best known for his '80s hit TV show, "Benson" -- died Tuesday at his L.A. home from complications of prostate cancer ... according to his wife, Donna.

Guillaume won the Emmy for lead actor in a comedy for playing sarcastic, wise-cracking butler, Benson DuBois, on the hit ABC show. "Benson" was a spin-off from "Soap." He won a supporting actor Emmy for that show.

He was also the voice of Rafiki on Disney's "The Lion King" -- and Isaac Jaffe on Aaron Sorkin's "Sports Night."

Throughout his career, Guillaume defied racial stereotypes with his characters on TV and in theater. He earned a 1977 Tony nom for "Guys and Dolls" ... and was the first African-American to play the title role in "Phantom of the Opera"

Robert was 89.