Lieutenant First Class Ellen Louise Ripley, was a civilian adviser to the United States Colonial Marine Corps and a hugely influential figure in humanity's encounters with the species Xenomorph XX121. She was the mother of Amanda Ripley-McClaren and the forebear of Alan Decker.
Beginning her career as a warrant officer with Weyland-Yutani Corporation's commercial freight operations, Ripley was assigned to USCSS Nostromo in 2122 when it encountered a single Xenomorph unintentionally collected from the moon Acheron (LV-426). The event led to the death of the rest of Nostromo's crew and the destruction of the ship, and Ripley's encounter with the Xenomorph would fundamentally alter the course of her life.

Later promoted to Lieutenant First Class and attached to the Colonial Marines as a civilian adviser, Ripley would go on to have several more encounters with the creatures over the following decades, before eventually sacrificing herself on Fiorina "Fury" 161 to put an end to the Alien menace once and for all. Her exploits ensured that she was well-known among groups and individuals that dealt with the Xenomorph for decades, even centuries, after her death.