Qixotl

Mr  was the pseudonym of a humanoid of undetermined species. He held an auction on Earth in the late 21st century. The sole item for sale was the Relic, whose existence he learned of while stranded on Dronid. During the course of the auction, Qixotl was killed by the Krotons, but recorporated by the Celestis in exchange for the Relic. The Eighth Doctor recognised him as someone who had betrayed him in prior incarnations by trying to sell him to Antiridean organ-eaters and, two regenerations before that, by turning him over to an "Embodiment of Pure and Irredeemable Evil". (PROSE: Alien Bodies)

Behind the scenes
Lawrence Miles originally intended for Qixotl to be Drax.