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. When Missy activated the tanks, he realised she was going to kill him, but Missy taunted him saying that she wouldn't kill him until he said something nice. Despite Chang's pleas, Missy murdered him. (TV: Dark Water)