One of Dr Gero's creations. He is also one of the last victims of Cell's killing streak.
Android 16 is one of the many androids created by Dr. Gero as part of his vendetta against Goku, who defeated Gero's Red Ribbon Army in the past. Even after Gero (as Android 20) is defeated, the androids continue to pursue Goku and his crew. In Future Trunks' timeline, Sixteen does not exist.
Sixteen is not only visibly different from his companions, being significantly taller than Seventeen and Eighteen, but he is created differently as well. While Seventeen and Eighteen are humans modified with cybernetics, Sixteen is completely mechanical, which provides him many benefits, although it also presents weaknesses. Although he is not human, Sixteen is shown to be capable of taking on some human emotion (such as caring for animals), and is named an "imperfect" unit by Gero, because he is too peaceful.
He takes kindly to animals and humans, and proves to be a valuable ally to the Z Fighters in their battle against Cell. It is revealed that, although he does not enjoy fighting, he is stronger than Android 17, since he is able to take on Cell while the villain is in his imperfect form, in an attempt to defend Android 18. Android 16 was defeated at the hands of Perfect Cell, after he absorbed Androids 17 and 18, and was blown to pieces on the battlefield after he attempted to save Krillin and Gohan.