At the airlock on the planetoid,
Ash, a Weyland-Yutani android,
Was a Company tool
Who broke the quarantine rule,
Getting crew* and Nostromo destroyed.
*Of course, Ripley and Jonesy the cat survive.
See also Aliens: Sulaco Transmission.
Interesting fact: all the names of the androids in the Alien movies (plus that shitty abomination, Prometheus) are alphabetically sequential. In the first film was Ash; in the second and third films was Bishop; in the fourth film was Call; and, finally, in Ridley Scott’s aforementioned fecal dessert course of turd pudding and dingleberry pie, was David. There you go: A, B, C and D. So, don’t be surprised if there’s an Earl, Ellis or Ernest in the future. Luckily, Neill Blomkamp never got the chance to ass-rape the franchise into a Chappie-like abortion, and Ridley’s Alien: Covenant turned out to be a surprisingly worthy addition to the series.