The Headhunter

The Headhunter was a bounty hunter.

Biography
The Eighth Doctor and Lucie Miller encountered the Headhunter on numerous occasions. (BFA: Blood of the Daleks)

The Headhunter arrived on Phobos days before the Doctor and Lucie arrived there. The Headhunter fell off a bicycle and knocked herself out and didn't wake up until they had left. (BFA: Phobos)

The Headhunter was contracted to kill Lucie Miller and was given time travel technology in order to track the Doctor's TARDIS. (BFA: Human Resources)

The Headhunter and Karen travelled to 19th century Sweden, where the Headhunter's plan of destroying a pocket universe was stopped by Lucie and the Doctor. (BFA: Grand Theft Cosmos)

The Headhunter finally sacrificed her life to save the universe from the Eight Legs. (BFA: Worldwide Web)