Gus (Mummy on the Orient Express)

Gus was a computer, who had placed together a team of experts on the Orient Express to stop the Foretold, without the passengers knowing. Gus essentially had control of the entire train, being able to stop it and suck oxygen out of rooms. When the Orient Express blew up, Gus was presumably destroyed with it. The Twelfth Doctor later stated that Gus might have been part of a wider conspiracy, saying that Gus didn't like it when trying to hack him to find out who the real culprit was. (TV: Mummy on the Orient Express)