Androids have been an integral part of the Alien universe ever since Ash (Ian Holm) went berserk on the crew of the Nostromo. But few of the actors playing machines for an Alien film have achieved the level of mysterious tension achieved by the outstanding Michael Fassbender in Sir Ridley Scott’s latest, Prometheus. David is, on the surface, an android employed by string-puller Peter Weyland (Guy Pearce). But as