The Astounding She-Monster is a 1957 science fiction horror film starring Robert Clarke and directed, written and produced by Ronald V. Ashcroft. The film focuses on a scientist and a gang who have kidnapped a rich heiress and their encounter with an alien who has crashed to Earth. In the UK, it was released as Mysterious Invader. It was released by American International Pictures as a double feature with The Saga of the Viking Women and Their Voyage to the Waters of the Great Sea Serpent.