Exigius 12½, better known by his Earth alias Martin O'Hara or "Uncle Martin", is a Martian inventor whose spaceship crash-landed on Earth near Los Angeles in the 20th century. He was discovered by newspaper reporter Tim O'Hara, who offered the Martian shelter in his own house while stranded on Earth trying to repair his ship. As a Martian, Uncle Martin possesses several psychic abilities such as telepathy, telekinesis and chronokinesis. He also has access to advanced technology which allows him to create extraordinary devices, including a time machine.
- Uncle Martin was originally played by actor Ray Walston in the 60's television series My Favorite Martian. He was later played by Jonathan Harris for the animated series and by Christopher Lloyd in the Disney movie.