1. In late 1983 James Cameron met with David Giler and Walter Hill to discuss potential projects, the pair were interested to work with him after having read his script for The Terminator. Cameron pitched several ideas but none of them seemed to be of interest to Giler and Hill. Fortunately just as he was about to leave the subject of a potential Alien sequel was raised, and Cameron was asked what he would do if it was down to him. Drawing inspiration from an unsold script he'd previously written called "Mother", Cameron went into detail, and subsequently submitted a 40-50 page treatment (again re-using elements of his earlier manuscript). Giler and Hill loved Cameron's treatment, they commissioned him to write a screenplay, and Fox green-lit the project. Cameron was given the good news that Aliens was to go ahead on the same day he landed screenwriting duties for Rambo: First Blood Part II.
2. At this time Cameron's resume as a writer and director only showed his 1978 short, Xenogenesis, and the 1981 Piranha Part II: The Spawning (which gets a generous 3.5 on IMDB!). However, 20th Century Fox were so impressed with his uncompleted script that they agreed to put the project on hold whilst Cameron went off to direct The Terminator.
3. Initially everyone just assumed that Sigourney Weaver would jump at the chance of reprising her role as Ripley, but when she was first approached she wasn't keen at all. At first she wouldn't even discuss any offers from Fox. She point blank turned them down and said she feared that any sequel not involving the original production team would be sub-par and that her character would likely be poorly written. So after Cameron completed his script it was sent to her in the hope to win her over. Weaver had strong concerns about the level of gun violence, later saying:
"It's hard for me, morally, to justify being in a movie with so many guns ... I give money to anti-gun legislation. I never even go to see movies with guns."However, she also said that she was very impressed by the strong focus on Ripley, the mother-daughter bond between her character and Newt, and the incredible precision with which Cameron wrote her character, so she finally agreed to enter negotiations for reprising the character.
4. Salary negotiations with Sigourney Weaver were now holding the production up, and so Fox asked James Cameron to work on an alternative script which would not feature Ripley. Cameron refused, and said that he felt the series is about Ripley and wouldn't want to make the film without her in it. However, after the release of The Terminator, Cameron's star was in the ascendency and he wouldn't wait forever before moving on to a different project, so he set a deadline - if Weaver's contract negotiations were not completed by the time he and Gale Anne Hurd (recently married) returned from their honeymoon, he was out of the project.
When the newlyweds returned, no progress had been made. Not wanting to give up on the project, yet wary of the deadline scenario he himself had created, Cameron devised a scheme. He called Arnold Schwarzenegger's agent for an informal chat and told him that, thanks to his new found standing in Hollywood, he had decided that he would make Aliens entirely on his own and would be writing Ripley out as his name was enough to sell the movie now. As Cameron had anticipated, Schwarzenegger's agent immediately relayed the information to his colleague, who just so happened to represent Sigourney Weaver! Weaver's agent quickly contacted 20th Century Fox's Head of Production, Lawrence Gordon, and wasted no time in finalising Weaver's deal.
5. H.R. Giger was not invited back to work on the sequel as both Cameron and visual effects supervisor Stan Winston theorised that the only new design would be for the Alien Queen, and Cameron had already penciled out many detailed drawings. However, once he got underway Winston made several changes to the look of the actual Alien itself, most notably Winston's Aliens had hands with three 'fingers' as opposed to six on the original movie's models.
6. Hicks was originally played by James Remar, but Michael Biehn replaced him a few days after principal photography began, due to "artistic differences" between Remar and Cameron. Biehn got the call on a Friday night asking him to take over the role, and was in London to start filming on the following Monday morning. Remar still appears in the finished movie in scenes he shot when he is in full armor. As whilst he is facing away from camera it's impossible to tell the difference between the two actors.
7. The knife trick scene was not included in the original shooting script. According to Lance Henriksen, the adding of Hudson's hand to the knife trick was discussed on set with almost everyone... except for Bill Paxton, who had no prior warning until the scene was shot.
8. Carrie Henn had never acted before she landed the role of Rebecca 'Newt' Jorden, yet despite her lack of acting experience she got second billing to Sigourney Weaver. More surprising is that she has never acted since Aliens. At last notice, she was a schoolteacher in California.
9. James Horner was tasked with composing the score for the movie, but his busy schedule only allowed for him to work on the film for a maximum of 6 weeks. After arriving in London on the agreed date, Horner discovered that the movie was still shooting, and editing hadn't even begun. After three weeks he'd just about given up hope of ever beginning when the phone rang to say he would finally have access to footage and could begin work. Many years later Horner revealed that because he had such little time to write the musical score he was forced to cannibalise some of his previous scores, 'borrowing' elements from his Star Trek II: The Wrath of Khan and Star Trek III: The Search for Spock scores, as well as adapting a rendition of "Gayane Ballet Suite" for the main and end titles.
Horner also revealed that Cameron was so stressed out during post-production, thanks to all the delays and his growing work load, in fact the movie was only completed 7 days prior to it opening in cinemas - this meant that all press screenings and advance showings were cancelled. Horner felt that the tensions between them, and his hurried finished score, would mean that he and Cameron would likely never work together again. However, the pair reunited for Titanic (which won the Oscar for Best Music, Original Dramatic Score), and again for Avatar.
10 Aliens was nominated for seven Academy Awards, including one for Horner's score! But the most prominent Oscar nomination was for Sigourney Weaver as Best Actress In A Leading Role - this was the first such nomination for any sci-fi or action film.
10 things you may not know about Alien
Follow Geek Dave on Twitter