Instead of following a predetermined path, the artificial intelligence of the Alien has been programmed to actively hunt the player by sight, sound, and smell. The Alien A.I was programmed with a complex set of behavioral designs that progressively unlock as it encounters the player to create the illusion that the Alien is learning from its encounters with the player and adjusting its hunting strategy appropriately. This includes the ability for the Alien to investigate "secondary sources" of disturbances. For instance, if it notices a locker or air lock is open, the Alien will search for who opened it.
Twentieth Century Fox provided the Creative Assembly with three terabytes of archived data related to Alien (1979), including notes on prop and set design, behind the scenes photos, videos, and the movie's original sound effect recordings, to help Creative Assembly authentically re-create the atmosphere of the movie. Among the source material provided by Twentieth Century Fox, was the movie's original musical soundtrack, to which the developers re-recorded several of the original cues with a full orchestra, including some of the musicians who worked on the first movie's soundtrack.
Most of the characters from Alien (1979) appear in the downloadable content (DLC) for this game, which includes two bonus missions called 'Crew Expendable' and 'Last Survivor', both of which take place aboard the Nostromo. The film's original cast members came back to voice their characters, with the exception of John Hurt (Kane) and Ian Holm (Ash). Hurt was unavailable due to scheduling conflicts, so his character was removed from the game. Holm couldn't reprise his role due to serious health issues, but allowed the makers to use his likeness and recast the role with Dave B. Mitchell.
The Alien was designed to look similar to H.R. Giger's original design for the creature from Alien (1979), including the semitransparent head with visible skull underneath. The developers altered the Alien's design to feature recurved legs as opposed to the more humanoid legs the monster had in Alien (1979), in order to provide the Alien a walk cycle that would hold up to scrutiny during longer encounters with the player.
The Alien emits vocalizations for which the player can listen to gain understanding of its current intentions. A scream may indicate that the creature is about to attack, while other sounds may indicate the Alien has seen something, is searching, or has lost all trace of its prey.