The Corsair

The Corsair was a Time Lord and friend of The Doctor on Gallifrey.

He is known to have gotten a snake tattoo applied to every regeneration during his lifetime, and was also said to have changed genders (presumebly by regeneration) more than once. The Doctor described him as a "bad girl."

The Corsair died during The Last Great Time War; however, he stored a psychic message in a hypercube asking for help, as many other Time Lords also did. His hypercube, along with the others, was washed up by a rift in the Bubble Universe and obtained by the House entity. House used The Corsair's hypercube to lure The Doctor to the bubble universe, under the pretence of The Corsair still being alive and needing The Doctor's help, to try and capture The Doctor's TARDIS.