One of the earlier androids made by Dr. Gero, his only purpose was to destroy Goku. However, due to conflicts with Cell, he was never able to acheive this task. He loves nature and would rather do bird watching then actually fight anybody. Unfortunately though, we don't get to see much of Android 16 throughout the series because he was destroyed by Cell. However, we have him to thank for Gohan going Super Saiyan Level 2 after Android 16's head was crushed.

Trademark Abilities: N/A

This Android claims to be the strongest of them all, when in fact, Android 16 is the strongest. 17, along with 16 and 18, went on a mission to finally destroy Goku but was delayed by Cell's intervention in the matter. 17 was absorbed by Cell and so he is never seen again from that point until Dragonball GT starts. Android 17 was also the one who destroyed his creator Dr. Gero (Android 20).

Trademark Abilities: N/A

Android 18 is powerful as she is beautiful. She even made Vegeta eat his own words during their battle. She is brothers with Android 17 and, like him, started out human before being made into an Android. Android 18 was also on the mission to destroy Goku but eventually was absorbed by Cell, making him Perfect Cell. She was regurgitated when Gohan landed a nasty blow to Cell's gut and she then married Krillin and had a daughter named Marron.

Trademark Abilities: N/A

Not much is known about this Android other than the fact that he's fat and he can absorb energy much like Android 20. He has small red crystals in his palms that allows him to suck up Ki blasts to add to his own power and to drain another's power level from grabbing their wrists. He was eventually destroyed by Vegeta after 19 had his hands ripped off and then shot with the Big Bang Attack.

Trademark Abilities: Absorb Energy

Android 20 is indeed Dr. Gero. He started out as an evil mad scientist who held a grudge against Goku. After Goku destroyed his entire Red Ribbon army, he created Androids bent on destroying him and also made himself into one to become a more formidable opponent. Like Android 20, he has the red crystals on his wrists used to absorb energy. Dr. Gero was destroyed by his own creation, Android 17, after he had reactivated him.

Trademark Abilities: Absorb Energy