The King’s Voice
While Kurt Russell didn’t appear in the film, his voice definitely did. In the scene where Forrest was showing off his dance moves, Kurt Russell was doing the voice recording for Elvis Presley. For reasons unknown, the role wasn’t credited.
Kurt Russell has acted with Tom Hanks before, back when he was just ten years old in a film titled It Happened at the World’s Fair. He also played the character of Elvis in a 1979 film of the same title, which earned him an Emmy nomination.