The Astounding She-Monster is a 1957 science fiction horror film starring Robert Clarke and directed, co-written and produced by Ronnie Ashcroft for Hollywood International Productions. The film focuses on a geologist, a gang which has kidnapped a rich heiress, and their encounter with a beautiful but deadly female alien who has crashed to Earth. In the UK, it was released as The Mysterious Invader. The film was released in American theaters on 1957 by American International Pictures on a double feature with Roger Corman's The Saga of the Viking Women and Their Voyage to the Waters of the Great Sea Serpent.

Robert Irby Clarke was an American actor best known for his cult classic science fiction films of the 1950s. In succeeding decades he appeared in more conventional television, and in The King Family Show, a variety show based on the family of which his wife Alyce King Clarke was a member.