Numbuh 1 is first seen in No P in the Ool and introduced as the (then) leader of the Kids Next Door. While the rest of his team is content to play in the kiddie pool, he takes action and says his catchphrase, "Kids Next Door, Battle Stations!" He is the only member to be focused on the mission, but ended up destroying the pool.
Numbuh 1 leads his team on the beginning of the C.A.K.E.D. saga, which also introduces one of his biggest enemies, the Delightful Children from Down the Lane. He first seems to be in control, but ends up being the piñata and almost gets shot during Pin the Tail on the Donkey. He suggests to Laura to open the red present, which says "Kids Next Door, Battle Stations!" and leads them to victory.