Very little of Mirris' background is known, except that during her childhood she had multiple fetuses fathers. As an adult she became an Administrator and like all other Aschen showed no signs of emotion. In 2004, she had a spy among the Pack that would secure an alliance between the Tau'ri and the Pack. She was responsible for the creation of a biological poison and planned to send it to Earth, secretly sterilizing and thus eradicating the human race. In a timeline where her plan succeeded, the pathogen rapidly mutated and nearly resulted in mass sterilization across the galaxy, with the last remnants of Stargate Command including Jade O'Neill and her father Jack O'Neill who was the commander of the Resistance.
With the aid of recently-discovered Ancient time-travel devices, Jade and Jack were able to travel back in time to the year 2004, working with SG-1 to stop the Aschen plan, with the two Jacks managing to kill Mirris and destroy her spaceship. (SG1: "Relativity")