Guest Stars Robert Duvall as Louis Mace William O'Connell as The Creature Douglas Henderson as Dr. Tillyard Howard Caine as Leon Chambers Henry Brandon as General Crawford Uncredited Roy Jenson as Gunman Vic Perrin voices Soldier Bob Johnson voices Loudspeaker Person Bob Johnson voices Chopper Pilot Dean Smith as Second Creature Christopher Riordan as Young Doctor Roy Olvera as Mexican Guitarist