If you were to ask every fan of sci-fi cinema to list the genre's ten most iconic characters, at least 99% of them would mention Sigourney Weaver's Ellen Ripley. Of course, a lot of people thought that the Alien franchise couldn't succeed without its legendary figurehead, and while they were definitely correct in the case of the Alien vs. Predator crossovers, Ridley Scott's prequels Prometheus and Covenant still did a solid job in expanding the mythology.