Alien was released in 1979, and Aliens in 1986. All of the movies in this series, including Alien 3 (1992) and Alien Resurrection (1997) were science fiction horror flicks. We include them here, instead of the sci-fi section, because frankly they scared us. The 1979 movie was both a box office and critical success, actually earning a number of awards. The 1986 movie did even better. All films starred Sigourney Weaver as Ellen Ripley.
In the 1979 movie, a spaceship called the Nostromo is on the way back to earth is asked to investigate a strange signal coming from a nearby planet and alien ship. While exploring the ship, they find a chamber full of eggs. One of the eggs hatches, attacks one of the crew, and all hell breaks loose from there as the alien hatch-ling begins killing off the crew.
Aliens (1986) finds the only surviving crew member of the Nostromo, Lt. Ellen Ripley (Weaver), waking up after 57 years of hyper-sleep. Ripley is shocked to find out that the planet from which she had escaped was being tera-formed, and that the crew on the planet could no longer be reached. The rest of the movie was about Ripley's return trip to the planet with a group of die hard Marines, who fight for their lives as the aliens pick them off one by one.