In the Manga/Anime
Android 19 is an overweight doll-like android with a clownish outfit. He is programmed to kill all the Z-fighters, Goku being his most important target. Android 19 was one of the later models Dr. Gero built, his 19 to be exact, due too his previous creations, Androids 17 and 18, not listening to him when he gave them orders. To fix the issue of disobedience Dr. Gero made Android 19, and himself, into less powerful but energy absorption type Androids. This allowed them to absorb any energy blast shot at them by placing their hands on it or absorb their opponents energy directly by grabbing them, this is demonstrated when Goku fires a Kamehameha wave at Android 19.
We first see Android 19 fighting with Goku as a Super Saiyan. At first it seemed that Goku was vastly stronger but early into the fight his heart virus that he caught in his space kicked in. Goku became slower, weaker, and eventually he lost his Super Saiyan status. Android 19 took Goku by the throat and started to absorb his remaining energy. It seemed that Android 19 had won but to his, and everyone’s, surprise Vegeta kicks Android 19 off Goku. Vegeta transforms into a Super Saiyan and kills Android 19 with his Big Bang Attack.
Android 19 has appeared in various Dragon Ball video games as a boss or as a playable fighter. In both cases Android 19 uses his unique energy absorption technique to feed of the powers of his opponents.