The first thing you notice about Sigourney Weaver is her height. Though 5ft 11ins is not extraordinary in itself, it gives her a domineering physical presence, which doesn't match her manner – amicable, understated, unstarry.
She sits down, looking not that much changed at 62 from the space-travelling heroine she played in Ridley Scott's Alien, aged 30. Yet even with the easy-going smile and the soccer-mom outfit (fuschia-pink shirt, jeans, sensible flat sandals) you can imagine her, if angered, pulling out an alien-zapping Bazooka.
Perhaps it is the legacy of her breakthrough role. She has crammed 57 films into the decades since, working with Roman Polanski, Ang Lee, and a host of other serious directors. Yet for many of her fans, she will always be best known, and most loved, as Lieutenant Ripley in the Alien quadrilogy.
She is quick to point out that "I've only done five science-fiction films", but each has been considered groundbreaking in its own right, which might be why she is sometimes seen as an unofficial ambassador for sci-fi.
Before Alien,a female lead in a sci-fi film was about as rare a sight as a snow-leopard in summer. A woman who became the only survivor on board a space-ship filled with swaggering men who are picked off, one by one, by a mutating killer alien, was even more unusual in an era defined by the red-blooded heroism of Han Solo.
As a result, Weaver is credited with bringing feminism to Hollywood and, beyond the quadrilogy, she has continued to play variations of the brainy, ballsy, "strong woman" survivor. There was her feisty zoologist Dian Fossey in Gorillas in the Mist, the agoraphobic psychologist in Copycat and the principled scientist in James Cameron's Avatar. Next month she will play a supporting role as a no-nonsense assistant district attorney, opposite Woody Harrelson's renegade cop, in Rampart.
As typecasting goes, the strong woman stereotype can't be a bad ghetto to be stuck in? Weaver is not so sure about the feminism theory behind Alien. She thinks Ripley was a shrewd plot surprise created by studio executives at Fox whose noses were led by the box-office, not Girl Power. "I don't think the producers were feminists. In the original script, they were all men. I think they thought, 'let's change it up and make the survivor a woman because no one will ever think the survivor will be a woman'."
What Alien and Ripley became was a mirror for the gender shifts taking place outside Hollywood: "I think it was taking the pulse of society at that moment; we were another expression of how our world was changing. Women were agitating to be in the army, to work in warehouses and as truck drivers."
All the more remarkable, then, that Alien has endured so well. In 2008, it was ranked among the top 100 best sci-fi films by the American Film Institute. For Weaver, this comes down to Scott's ability to create an "everyman character".
"We worked very hard together, and I certainly credit him in making Ripley an everyman character, not just a damsel in distress, but a character who is not giving up. Cameron (who directed the follow-up, Aliens, in 1986) was also a breath of fresh air. He is a champion of strong women who never thinks in terms of gender characteristics."
Even so, she is not denying the reality of gender stereotyping in film or its impact on actresses' careers. The glass-ceiling is there for actresses as it is for women in all sections of society, she says, but it is a more textured, less depressing picture now than it used to be, when her mother, the English actress, Elizabeth Inglis, sacrificed her career for raising a family. Weaver, by contrast, has been a working mother ever since her daughter, Charlotte Simpson, was born in 1990.
The making of Avatar, and its sequel, which is already underway, made her rethink the future of movies: its radical new technology meant that actors were performing in a blank space, acting without any diversions or distractions (the scenery and special effects were visible on monitors nearby). The experience was a gratifying one, more like a theatre rehearsal than the stop-start of conventional filming, and it also made her see the limited lifespan of 2D films.
"I think 2D is going to be like black-and-white soon because 3D is the natural way that people encounter life, so it's a revolution the way that Greco-Roman sculpture was after hieroglyphics.
"It's the future, but it will be a while before people can achieve 3D consistently in a way that puts you in a world of the story in a seamless way. That's the object: to immerse you in a world, not to trick you or entertain you. And that's why it's more important perhaps for a regular movie; you should be in their world – whatever they say and decide and think should mean more to you because you can't divorce yourself... I'm excited to go back to Avatar. I know the story that James Cameron wants to tell is so much bigger."
One of the striking aspects of Weaver's career is the way she oscillates between working with the giants of film-making and debut directors, often alternating serious dramas with eccentric comedies or action films. In fact, when a project appears too slick, she shies away, preferring the edgier, less flashy idea. Last month, at the Marrakech Film Festival,she judged the short-film prize and seemed genuinely excited to discover the preoccupations of a new generation of film-makers.
"I think I have a reputation for being totally game to do something I haven't done before, with people I haven't worked with before. I'm easily distracted by the next interesting thing. Then I look back at all the zigzags, and that's my career. I have gone 'this director looks interesting', and 'that's a cool story'.
"I like to be in mongrel, not pedigree films. Any time it's too blue chip, I get nervous. When it has the 'greatest' actors, the 'greatest' screenwriters, the 'greatest' directors, I turn off. I feel claustrophobic in something conventional."
Her projects after Marrakech are just as varied: Avatar 2 with Cameron, possibly Ghostbusters 3 with Bill Murray, co-starring with Robert De Niro in Red Lights, a film about paranormal activity and a wonderful-sounding radio project: "It's a series highlighting the American song. I'm one of the actors in it. We're trying to raise the money to do 13 half-hour dramas, based on a song chosen from each decade."
Choosing the next project, she says, has very little to do with the character. It's about the story, and the team she will be working with. So it is surely a disappointment to her, given her admiration for Scott, that she has no part in his Alien prequel, Prometheus, which is scheduled for release this year.
There seemed to be brewing tensions between Weaver and Fox studios for some time. She was quoted as saying that she would liked to make one last Alien story where the crew went back to the planet, though she thought it unlikely that Fox would agree to cast an action hero over the age of 60. She no longer subscribes to this view, though she readily admits to radical differences in opinion: "Fox and I disagreed on how the franchise should continue. But I'm glad it's Ridley doing it, and I'll be as curious as anyone, or maybe more curious, to see it. I think he took my suggestion. Fox wanted to go to earth and I said: 'That's so boring. Who wants to see aliens on earth?' I said 'go back to the planet'."
The crew of the Prometheus spaceship, who include Guy Pearce, Michael Fassbender and Charlize Theron, will apparently discover a clue to the origins of mankind which leads them into the outer reaches of space, so at least Weaver has made her mark in the storyline. Still, an Alien mission with no Weaver on board. It sounds like sacrilege. Weaver shrugs. "That's show-business, she says. "I don't take it personally."
'Rampart' is released on 10 February