"That was most invigorating."
Numbuh 84, or Lee, is a 7 year old boy who attended KND training academy with Sonia 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 blue and orange striped shirt, blue shorts, brown shoes but with no socks and a brown ushanka that covers his eyes. Lee constantly uses the word "cool", saying it multiple times in almost every episode in which he appears, although his vocabulary is far from limited.
He is often seen with Sonia, 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!"