Android 18 is a human turned android created by Dr. Gero with her twin brother Android 17 to defeat Goku. She is cool, calm, collected and intelligent. When her brother killed Dr. Gero, they went on with newly activated Android 16 to try and defeat Goku.
However, in the process, Android 18 ended up falling in love with Krillin. They got married and had a daughter together named Marron.
She first maintained a cool but distant attitude towards Goku after marrying Krillin but later she warmed up to him and even helped him out during fights. She has also maintained a good relationship with the other Z Fighters, their wives, and their children.