The Alien Queenliving on Archeron, formerly LV-426, was discovered by Ellen Ripley during the evacuation of the planet.
After rescuing Newt, Ripley stumbled onto the nest where the Queen was actively laying eggs. Ripley destroys the eggs with a flamethrower, enraging the Queen. The Queen detached from her ovipositor and began chasing the two.
Ripley and Newt took an elevator to the platform to wait for Bishop to arrive in the dropship. He finally did and they escaped the doomed planet which exploded moments later.
However, the Queen stowed onboard and tore Bishop in half. Ripley climbed into a Power Loader and fought the Queen until the two toppled over into the hangar airlock. Ripley managed to climb out, while the Queen was trapped under the Loader. Ripley managed to trip the airlock doors, jettisoning the Queen into space.
It is later found out in Alien³ that the Queen managed to lay an egg in the Sulaco which produces a Queen embryo that impregnates Ripley.