Lee, a.k.a. Numbuh 84, is a 7 year old boy who attended KND training academy with Numbuh 83 and Tommy in Operation: T.R.A.I.N.I.N.G.'' and later became the "Tactical Yo-yo Specialist" of Sector W. He usually wears a a blue and orange-striped shirt, blue shorts and a snow hat that covers his eyes. Lee constantly uses the word "cool", and says it multiple times in almost every episode in which he appears, although his vocabulary is far from limited. He is often seen with Sonya, and was even seen holding hands with her in ''Operation: Z.E.R.O.'', where they went on a tour of the Kids Next Door Seriously Cool Museum of Artifacts and Stuff. Lee was last seen in the series finale ''Operation: I.N.T.E.R.V.I.E.W.S., where his last line was "Cork it, Harvey(363)!"
Lee and his favourite toy, Yo-Yo
He physically resembles Numbuh 4, as Sonya resembles Numbuh 3. like how Sonya is a little taller than Lee like Kuki is taller than Wally.