Android 18

Android 18 is the twin sister of Android 17 and a hero in Dragon Ball Z and Dragon Ball Z Kai series.

She was absorbed by Cell in order to reach his perfect form, but was then saved by Gohan after kicking Cell so hard that it made him throw up Android 18. She was then protected by Krillin during the battle between Gohan and Cell, because of that 18 fell in love with Krillin and the two eventually got married and had a daughter named Marron.

Background
Android 18 was created by the mad scientist Dr. Gero of the Red Ribbon army. Though called an Android in the english dub, she is in-fact a cyborg, formally human enhanced with nano-technology to be made into a man-made super-human. Her original human name was Lazuli. Lazuli was kidnapped with her brother Lapis, who would become the Android 17 and the two were just  a couple of the many civilians Gero had used as gunia-pigs for his research.

Android 18 was awoken from her stasis by Gero to take on the Z Warriors. 17 killed Gero shortly after activation, resenting the notion of serving someone who had held power over him and his sister all his life. Though 17, 18 and the Android 16 were all still set on their primary programing, the death of Son Goku, they were all much more anxious to live life to the fullest and proceeded on a rampage of abject destruction and vice gratification. After being attacked by the other android Cell, and freed, 18 comes to the conclusion that she is not the enemy of the Z fighters or the world and becomes an on again off again ally. By the following saga against Majin-Buu, Android 18 decides to pledge her efforts to aid the Z-Warriors to help save the planet.

Personality
Even when crossing over from villain to hero Android 18 remains stoic and sarcastic in most circumstances. Android 18 cares for her daughter Marrion, her brother and eventually Krillin, but is otherwise less than invested in those around her. Like her brother, Android 18 is all about looking out for herself or those directly related to her. She view violence as fun at first but eventually tires of it, not for moral reason but imply because she become jaded to it.

Relationships

 * KRILLIN: The two first met when 18 and 17 were beating up the Z-Fighters, though neither of them harmed Krillin, 18 did kissed him in the check and said "See you soon". Because of that Krillin started falling in love with 18. Later when Bulma invented a button than can destroy 18, she gave it to Krillin in order to destroy her, but Krillin refused and destroyed it. During the battle between Gohan and Cell, Krillin protected 18 so she wouldn't get hurt. After the battle was over, Krillin wished that 17 and 18's bomb's inside them would be destroyed. Because of that 18 fell in love with him and the two eventually got married and had a daughter named Marron.


 * ANDROID 17: Android 17 is 18's twin brother. The two get along very well, however 18 does call him a child sometimes. After the Cell saga the two of them never interacted anymore. But in Dragon Ball GT they interacted in the Super 17 saga, where she helped Goku defeat him so he wouldn't kill anyone else, but was very sad when she did so.


 * GOKU: 18, 16, and 17 were originally programed to kill Goku, but didn't do it after Gohan and the Z-Fighters defeated Cell and saved them. When Goku came back 7 years later, 18 and him didn't interact that much. Goku was also shocked when he learned that 18 could have a baby.


 * GOHAN: Though the two never interacted that much in the series, it was Gohan who saved 18's life when he kicked Cell so hard that it made him throw up 18. So its most likely that she thanked Gohan for that. 18 was also very happy when she found out Gohan killed Cell, probably cause she was scared of Cell. Also when Gohan about to kill Super Buu, Buu told him that if he did then all his friends, which include 18, would die as well. Because of that Gohan didn't have the guts to kill him.