343 Guilty Spark (often called Nanny, and formerly called R2-D2) is a robot built by ancient people from A Long Time Ago in a Galaxy Far Far Away. He became Master Chief's nanny when he found Halo. But he hated him, and blew him up after he tried to kill him.
343 Guilty Spark was very guilty, as he often killed anyone who went on a Halo. Master Chief was so awesome, he didn't kill him, and just nagged. He only attacked because he was trying to blow up Halo. He doesn't like him anymore, probably because he blew him up with a SPARTAN LASER!
343 go boom.