Muldwych

Muldwych spent 1,000 years stranded on Mount Kukoeuk on Ant'ykhon. He assisted Bernice Summerfield and Ace with the Doctor's TARDIS. (NA: Birthright)

He gave the Doctor time rings for Bernice and Jason Kane's wedding.

There is some suggestion that he is a future or alternate incarnation of the Doctor, possibly Merlin. (NA: Happy Endings)