In Prometheus, Michael Fassbender plays the android David.
David is a synthetic human created by Peter Weyland and assigned to support the Prometheus expedition. He maintains the ship while its human crew is in suspended animation, studies alien technology, and interacts with the mission’s scientists and engineers.
The character is deliberately modelled on the appearance and behaviour of a human being, but the film repeatedly explores the difference between artificial life and its creators. David’s curiosity, resentment, and interpretation of Weyland’s instructions drive several major events in the story.
David is part of the same broad android tradition as Ash and Bishop from earlier Alien films, but he is a separate character. Walter, another Fassbender android, appears in Alien: Covenant, the later film that continues Prometheus’s storyline.