Earl Sigma was a blues player from Earth who played blues songs on Terra Alpha. However, this style of music was deemed "unhappy" and outlawed, leaving him with no means of income to buy a way off-planet, stranding him there. He helped the Seventh Doctor through the Kandy Man's kitchen, snipers and loads of other dangers.
Behind the scenes Edit
Sigma was not Earl's last name, but a designation given by Terra Alpha to people from other planets.