Archibald Angelchrist

Professor Archibald Angelchrist helped the Eleventh Doctor defeat the Squall in London in the year 1910. Ten years after helping the Doctor send the Squall back through the rift, the Doctor, Amy and Rory returned with Arven, who had been given a new body, and left him to live with Angelchrist. (PROSE: Paradox Lost)

Behind the scenes
Author George Mann, who created Angelchrist, has featured the character in several short stories published by Obverse Books, such as The Albino's Revenge in the 2012 Obverse collection Zenith Lives! which, in turn, was a series of stories featuring a villain from the long-running Sexton Blake novels and short stories. He also features in Mann's Newbury & Hobbes series of detective novels. This does not necessarily mean all these stories are set in the DWU. Since Doctor Who allows for the existence of parallel universes, it's possible that there are multiple versions of Angelchrist or that Paradox Lost is set in an alternate timeline.