Nigel usually wears a red turtle-neck sweater, grey shorts, white socks, and brown shoes, which acts as rocket shoes from him when he clicks his heels together. He is seldom seen without his sunglasses and most noticeably of all, he is bald. Before he lost his hair it was proven to be brown in Operation: F.O.U.N.T.A.I.N.
Numbuh 1 is described as the sternest, workaholic member in Sector V, as he would rather go on mission than spend his day-off at the beach as seen in Operation: B.E.A.C.H. and Operation: B.U.T.T.. Alongside Numbuh 5, he is considered the only one with common sense on his team. As the leader, he is quick to action and quite resourceful, but tends to be paranoid to the point of stretching the truth and using his imagination when analyzing a potential adult threat.
- Father: Monty Uno (KND retired member, Numbuh 0)
- Mother: Mrs. Uno (KND retired member, Numbuh 999)
- Grandfather: Grandfather
- Uncle: Benedict Uno/Father
- Cousins: Numbuh 10 & Delightful Children From Down The Lane/Sector Z (adoptive)
Future Wife: Rachel T. McKenzie (Numbuh 362)
His codename is a reference to his last name, Uno, the Spanish and Italian words for one.
- He is the only member of Sector V who doesn't have a brother or sister.
- Numbuh 1 was shown to be a lousy singer, but sings rather well in Operation: L.O.V.E.
- He is afraid of bygs and shots.