'Swordfish' was a Time Lord encountered by the Eighth Doctor and his companions onboard an ancient TARDIS they found floating in the vortex.
Originally a preeminent 'psychosurgeon' on Gallifrey, he treated a young Caleera, conducting the initial interviews and eventual surgery on her that suppressed her burgeoning psychic abilities. He took great pride in his work, in restoring her to 'normal', and felt he'd done her a great service. Caleera bore a grudge for years, and after she was manipulated by the rogue Time Lord known as 'the Eleven', she used her returned abilities to punish him. She then 'recruited' him along with two other Time Lords to act as 'helpers' in her efforts to expand her abilities even further.
By the time the Doctor arrived, he had taken to calling himself 'Swordfish', and had been driven insane through exposure to the Time winds, since the TARDIS had badly degraded, losing it's outer shell completely. He took on the role of a servant to 'Lord Stormblood' and 'Lady Sepulchra', his fellow Time Lord captives, and was responsible for the prisoners they kept as test subjects. He remembered enough to still help with the experiments, and that it used Caleera's own psychic powers. Once Caleera was free, she lowered the TARDIS shields, allowing Stormblood and his companions the death they longed for, sending them falling into the vortex. (AUDIO: Scenes From Her Life)