Ash in Alien
One of the many villains disguised as good guys in the realm of science fiction is Ash (Ian Holm) from the 1979 film Alien. In the Ridley Scott-directed movie, Ash was introduced as a by-the-book science officer of the ship Nostromo. But when Ash broke quarantine by allowing crew member Kane (John Hurt) back on board after the latter was infected by an alien life form, some viewers felt that there’s something off about Holm’s character.
In the third act of the movie, it was revealed that Ash is not a human, but actually a Hyperdyne Systems 120-A/2 android, a sleeper agent who is acting upon secret orders to bring back the alien lifeform and to consider the crew and the cargo as expendable.