#16 was an experimental android built by Dr. Gero. Unlike #17 and #18 he is completely mechanical, and he is more powerful than them. He can also sense power levels unlike #17 and #18.
Android 16 is very different from any of Dr. Gero's
other Androids. Unlike the other Androids, he has no desire to cause any havoc to anybody other than Goku
, whom he is programmed to find and destroy. While his closest Android companions, 17
spent most of their time after being first introduced killing and stealing from people just for the fun of it, Android 16 is the polar opposite to them in personality, often seen caring for small animals in the wild. He only wants to kill Goku because he is programmed to do so.