4 movies: Alien / Aliens / Alien 3 / Alien Resurrection

Alien: After a space merchant vessel perceives an unknown transmission as a distress call, its landing on the source moon finds one of the crew attacked by a mysterious lifeform, and they soon realize that its life cycle has merely begun.

Aliens: Ellen Ripley is rescued by a deep salvage team after being in hypersleep for 57 years. The moon that the Nostromo visited has been colonized, but contact is lost. This time, colonial marines have impressive firepower, but will that be enough?

Alien 3: After her last encounter, Ellen Ripley crash-lands on Fiorina 161, a maximum security prison. When a series of strange and deadly events occur shortly after her arrival, Ripley realizes that she has brought along an unwelcome visitor.

Alien Resurrection: 200 years after her death, Ellen Ripley is revived as a powerful human/alien hybrid clone. Along with a crew of space pirates, she must again battle the deadly aliens and stop them from reaching Earth.