Trevor Sigma

Trevor Sigma worked as the official Galactic Censor. The 'Sigma' designated that he was from a planet other than Terra Alpha.

Biography
Trevor was a citizen of Earth who came to Terra Alpha to investigate the colony planet. When he did, he had to stay for ten years. He distracted Joseph C so the Seventh Doctor could talk to Helen A. He discovered that Helen A had gone mad with power and was killing anyone who wasn't happy. With the Doctor's help, he removed Helen A from power by starting a revolution.(TV: The Happiness Patrol).