Numbuh 88 is a Kids Next Door spy, apparently one of the best. He only appeared in Operation: G.R.A.D.U.A.T.E.S..
While spying on Father in his mansion disguised as a dog, he was discovered by Father when he bit on the Animalization Ray wires. Father pulled on his tail which made the costume rip, and revealing Numbuh 88's face. He was the first victim of the Animalization Ray; however, he managed to get a message to the Kids Next Door Moonbase before being turned into a rooster.