Walter Fisher was the president of his planet. He was imprisoned when his government was overthrown, but the Doctor rescued him and brought him to Earth. Walter spent forty years on Earth, and was married to a human woman.
When the rightful government was restored, Walter was granted a pardon. The Fourth Doctor and Leela attempted to deliver news of the pardon to Walter, but he was killed by an assassin before they could find him. (PROSE: The Sooner the Better)