Stefan Arngrim

He has the distinction of being the only one of the two boys who appeared on Irwin Allen's TV series to be doubled. He and Bill Mumy were the only boys to appear in Allen's series, and Mumy had the distinction of being the only one of the two boys to appear as his past self (in the Perdidos en el espacio (1965) episode, "Project: Earth"), in a flashback to the time of the Jupiter Two's original launch. But Stefan had to be doubled in the Tierra de gigantes (1968) episode, Wild Journey (1970), because he had already gone into puberty and thus could not appear as his younger self.