Baltazar

Baltazar was a space pirate who had once been imprisoned on the prison planet Volag-Noc. Initially determined to compress the planet Earth into diamond, an act which would have killed off life on the planet, the Doctor and Martha Jones stopped him. Later, Baltazar went on to search for the lost ship, the Infinite via its data chips, and used the Doctor to track it down. He had a metal bird pet called Caw.

The Doctor refered to him as the "Scourge of the Galaxy". Despite this, Baltazar was notable for having a sense of humour (rare among the Doctor's opponents) and was seen poking fun at Martha and laughing while watching the Doctor awkwardly trying to pilot Caw's offspring, Squawk. (DW: The Infinite Quest)