Nigel Uno, known by his codename Numbuh One, is a fictional character and the leader of Sector V of the Kids Next Door. Numbuh One speaks with a British accent. He has an overprotective girlfriend, Lizzie. Numbuh One is usually the person who motivates Numbuhs Two, Three, Four and Five to act.

Numbuh One usually wears a red sweater, grey shorts and brown boots (which contain booster rockets, allowing for flight). He is seldom seen without his sunglasses. The Delightful Children from Down the Lane caused Numbuh One to be bald, though the method has not yet been explained.

Numbuh One is voiced by Ben Diskin.