Android 18 was created by Dr. Gero just like #17 and #16. She just like #17 showed no mercy and killed numerous humans and destroyed many cities with 17. Later on Cell absorbed her and completed his completion. After Cell self destructed she was spat out. After the Z Warriors killed Cell they wondered what they would do with her. They all agreed to get rid of her except for Krillion. who had fallen in love with her. They later wished for her to become human with the Dragonballs.
Later she married Krillion and they had a daughter named Marron. She was the only Android that survived.