War of the Colossal Beast, released June 20, 1958, is the sequel to The Amazing Colossal Man. Like its predecessor, it was directed by Bert I. Gordon and featured Lt. Col. Glenn Manning as the antagonist (this time played by Dean Parkin).
Upon hearing of several recent robberies of food delivery trucks in Mexico, Joyce Manning, Army officer Lt. Col. Glenn Manning's sister (though in The Amazing Colossal Man, his fiance said he had no surviving family), becomes convinced that her brother survived his fall from the Hoover Dam at the end of the first film. Along with Army officer Major Mark Baird and scientist Dr. Carmichael, she goes to Mexico to look for him.
It is discovered that Manning, now grown to 60 feet tall after being exposed to plutonium radiation, survived his fall from the Hoover Dam at the end of the previous movie, but he has gone insane and part of his face was left disfigured following his confrontation with the Army there, turning him into a zombie-like creature.
Not only has the plutonium radiation mutated him into a 60 foot disfigured freak, it also has reduced his vocabulary - he now appears capable only of uttering simple variations on "aarrrgh" (although he does manage a single strangled "Joyce!" at the movie's end).