According to Yaphet Kotto, Sir Ridley Scott told him to annoy Sigourney Weaver off-camera, so that there would be genuine tension between their characters. Kotto regretted this, because he really liked Weaver.
Sir Ridley Scott stated that in casting the role of Ripley, it ultimately came down to Sigourney Weaver and Meryl Streep. The two actresses had been college mates at Yale. Ultimately, Weaver was offered the job because Streep was mourning the death of her partner John Cazale at the time of casting.
Copywriter Barbara Gips came up with the famed tagline used in the posters and promotional materials: "In space, no one can hear you scream."
Director Sir Ridley Scott originally wanted to use animatronics (remote-operated puppets) to portray the Alien, thereby hoping to avoid the sight of a monster being obviously played by a man in a suit. Unfortunately, the special effects techniques at the time weren't sophisticated enough for what he had in mind, but he agreed to an actor playing the part after being introduced to Bolaji Badejo. Badejo was a graphic artist who was discovered at a pub by one of the casting directors. He was 208 cm (six feet almost 10 inches) tall with very thin arms, just what they needed to make the Alien look less human and more insect-like. He was sent for Tai Chi and mime classes to learn how to slow down his movements, and a special swing was constructed for him to rest on during filming, as he couldn't sit on a regular chair once suited up because of the Alien's tail. A suit was also made for a stunt man for more complex movements, but nevertheless, Scott kept the screentime of the Alien limited to hide its human configuration.
Ridley Scott: [mothers] The Nostromo's computer is named "MU-TH-UR". The incubation of the Alien has also been interpreted as a metaphor for pregnancy.