In 1979, Alien came out and Sigourney was in it with a bunch a guys. Nobody at that time expected the woman to be the hero, so that was a tradition that started.
“Actors use who they are to be someone else, but I would hate to ever think I'm playing myself. It's imagining being someone else that is the key motivating thing for me. So when people want to know about me, it makes me a bit unnerved.”