Tarlos

Tarlos was the son of Edwin. He was bored with his life and wanted to explore when the Second Doctor arrived on his home colony of Triketha and saved it, taking Tarlos with him afterwards. They travelled together for some time but when the Doctor attempted to return him home a few minutes after they left, he accidentally left him on the wrong planet and 48 years out of time.

Years later, Tarlos managed to return to Triketha, bringing with him a collection of endangered species, including the Toraxians. His ship crashed and the Toraxians escaped; having been stung, Tarlos remained in cryogenic stasis until he was revived by the Sixth Doctor. Tarlos was bemused that the Doctor couldn't remember him and presumed that the Time Lords locked his memories of him up. When the Toraxians change the entire colony population into more of themselves other than himself, Edwin, the Doctor and Constance Clarke, Tarlos helped the Doctor destroy the colony and the Toraxians and he kept his promise to rescue him and his father from the explosion.

The Doctor offered him one last trip in the TARDIS but he declined. Tarlos asked if he wanted to know about the memories that he'd been stripped of but the Doctor tells him that there's likely a reason he was made to forget but privately confided to Constance that one day he might be able to unlock those memories. (AUDIO: Colony of Fear)