Frobisher

Frobisher was a Whifferdill, a shape changer who travelled with the Sixth Doctor and Peri and then the Seventh Doctor for some time.

Frobisher was once married to another Whifferdill named Francine.

Meeting the Doctor
Frobisher first met the Sixth Doctor when he was a private investigator calling himself "Avan Tarklu". He came across the Doctor when an enemy of his, Dogbolter, placed a bounty on the Doctor. After infiltrating the TARDIS, instead of turning the Doctor in for the money, Tarklu decided that he liked the Doctor and helped him against Dogbolter. He then joined the Doctor on his journeys. He assumed the name of Frobisher because he felt that it sounded British and thought that the Doctor would like that. (DWM: The Shape Shifter)