Android 18 is a fictional character who first appears in the Dragon Ball manga created by Akira Toriyama, followed by Dragon Ball Z and Dragon Ball GT. No. 18 is a mass murderer in Future Trunks' timeline. A cybernetic human, #18 modified by Dr. Gero. She is often referred to in the original Japanese as a jinzōningen, which literally translates as "artificial human". She is not entirely an android; she refers to both herself and her twin brother as having been "constructed from a human base".

Spoiler

After Cell is defeated, Kuririn uses the Dragon Balls to wish for #17 and #18 to be turned into humans; Shenlong is unable to perform this task because of the unfathomable differences in power between him and the duo, so he wishes instead for their self destruct devices to be removed. Kuririn pursues #18 and, at some point, they marry and have a daughter named Marron. To clear up the heavily espoused misconception that #18 is a pure android and therefore could not have a child, Kuririn went on to explain to Son Goku during the World Tournament Saga that she was originally human but that Dr. Gero just "remodeled her a little bit."

(Source: Wikipedia)