Chang (Dark Water)

Dr Chang was charged with maintaining the Mausoleum in St Paul's Cathedral. He took care of the Twelfth Doctor and Clara Oswald when they were sightseeing in the Mausoleum and showed them 3W. He was the one who showed them dark water and what the 3W stood for. He also created an online link between Clara and Danny Pink. Despite his pleas, Missy killed him. (TV: Dark Water)