Earl Sigma was a blues player from Earth who played blues songs on Terra Alpha. He helped the Doctor through the Kandy Man's kitchen, snipers and loads of other dangers. After the Happiness Patrol and Helen A were deposed, Earl decided to stay and teach the people there the blues again. (DW: The Happiness Patrol)
- Sigma was not Earl's last name, but a designation given by Terra Alpha to people from other planets.