Dantalion

Doc Dantalion was a Birastrop doctor. He trained on humans in the 1970s, offering treatment to terminally ill rich people with no family, then dissecting them for study. He was captured by UNIT, but the Third Doctor convinced him to return in a thousand years, when humans would have morals more similar to his own. (PROSE: Where the Heart Is)

By the 30th century, Dantalion was a memory-sculptor. This meant he could alter or remove memories. He did his work in one of Earth's undercities. Dantalion removed Powerless Friendless' memories of his captain's treachery that had lead to the destruction of the Hith homeworld. He also removed Roz's memories of her former partner Fenn Martle's betrayal. He later restored both. (PROSE: Original Sin)

Dantalion was one of the guests at Benny and Jason's wedding in Cheldon Bonniface. (PROSE: Happy Endings)