Android 16 was created with the sole purpose of destroying Goku. Dr. Gero warned Android 17 and Android 18 not to awaken 16, as his programming wasn't complete. They awakened him anyway after killing Dr. Gero. As they left in search of him, they were confronted by Vegeta. 17 asked 16 to fight Vegeta, but 16 refused, saying he would only fight Goku. Initially he only wanted to talk about Goku (at one point mistaking 17 saying "Go too" for "Goku"). However, he soon became interested in birds and squirrels, and complained about the fighting scaring them away.
16 knew where Goku lived, and told 17. He also has the ability to sense energy signals, saying that Piccolo was just as strong as 17, which 17 refused to believe. When Cell came to absorb 17, 16 told 17 not to fight Cell. After Cell nearly killed Piccolo and beat up 17, he tried to absorb him, but 16 stopped him. Since he loved the world so much, he decided he would destroy Cell and save the world. He beat up Cell, as their power levels were equal, but Cell became stronger when he absorbed 17. Cell destroyed part of 16's head.
After Cell absorbed 18 and became complete, Krillin decided to take 16 to Capsule Corp so Dr. Brief could fix him. During this time, they discovered his bomb inside him, intended as a last resort so he could destroy Goku, and removed it, not trusting that he wouldn't still use it on him. However, when 16 met Goku at the Cell Games, he made it clear that he has chosen not to destroy him as he was programmed to. When Cell was fighting Gohan, 16 jumped on him and tried to self destruct to kill him, but as his bomb was removed this did not work. Cell destroyed 16's body. His head survived and told Gohan to fight Cell, and to protect the life on Earth for him. Cell killed 16 by stomping on his head.
He was never seen again following this, but as the Dragonballs have been known to revive artificial life (Android 8 was revived with all of Earth's inhabitants after Buu blew up the earth), it is likely he was revived along with the rest of Cell's victims. If so, he lived a life of peace on Earth until Kid Buu blew up the Earth, killing him again, but he was wished back again.