Sigourney Weaver is best known for her iconic role as Ellen Ripley in the Alien franchise, but she wasn't the only actress considered. Prior to landing the role in Alien, Weaver only had a couple of small TV credits to her name. When the popular sci-fi horror film was released in 1979, it wasn't very common for heroic roles to be portrayed by female characters.
In fact, Ripley wasn't originally written to be female (all of the character genders were ambiguous in the script). The fact this was Weaver's breakout role as a relative newcomer made the choice even more surprising. After Alien, Weaver ended up reprising Ripley for three sequels and she's generally regarded as a pioneer for actresses in similar roles. Though it's difficult to imagine anyone else besides Weaver as Ripley now, there were other actresses who were considered and even auditioned for the part.
Perhaps the most surprising actress considered for Ripley was The Devil Wears Prada star was just starting to find her stride in her acting career, which hasn't really featured any action roles. At the time, however, Alien's casting director Mary Goldberg felt Streep might be a good fit for the character. The Alien Anthology Blu-ray (via Syfy Wire) featured a deleted documentary clip in which producer Gordon Carroll explained that Goldberg suggested both Streep and Weaver for Ripley. Streep's actor partner John Cazale had recently ed away when she was under consideration, so Carroll decided it was best to let her grieve then pursue her for the movie.
Helen Mirren is another actress who almost played Ripley, and particularly ired the script's ambiguity when it came to the characters' sexes. In an interview for Vulture in 2010, Mirren mentioned her audition and her appreciation for the writing: "[The characters] all had these sort of asexual names, so when Ripley said or did things, you had no idea whether Ripley was a man or a woman..." While Mirren confirmed she auditioned for the film, it seems that producers or filmmakers decided she wasn't quite right for the role.
In addition to Streep and Mirren, The Alien Saga documentary mentions that actresses Katharine Ross and Geneviève Bujold, who were more established leads at the time, were also approached. Veronica Cartwright appeared as Lambert in Alien, though she had originally read the script for Ripley and thought she won that part when she got the call for the movie. In the end, the character went to Weaver, and the alien-slaying role made the actress a star.
