Numbuh 65.3, who's real name is Herbert, is a nerdy and overweight KND communications officer who regularly contacts Sector V. He appears in several episodes as a minor recurring character. He is voiced by Dee Bradley Baker. He first appeared in Operation: B.R.I.E.F., where he informs Sector V of a hit warrant on Numbuh 1, and shows them a physical model of the assassin, a living pair of underwear named Mr. White.

In Operation: B.E.A.C.H., Numbuh 1 contacts him asking for missions in order to get out of having to take a day off, but Numbuh 65.3 told him that there were no missions for him that day. In Operation: L.E.A.D.E.R., he calls while Lizzie is holding Numbuh 1's place as sector leader, and shows off his pocket protector to her. He was briefly seen at the graduation party in Operation: G.R.A.D.U.A.T.E.S.. He was one of the racers in the Toobathon in Operation: C.A.K.E.D.-F.O.U.R., and also featured briefly in Operation: C.A.N.Y.O.N. and Operation: H.O.L.I.D.A.Y..

In Operation: I.T., Numbuh 65.3 is shown asking Numbuh 362 to sign paperwork, and was later tagged by Numbuh 3, before tagging Numbuh 13 and then collapsing from exhaustion. In Operation: G.I.R.L.F.R.I.E.N.D., Numbuh 362 and Numbuh 1 suspect Numbuh 65.3 of being involved with the Splinter Cell, and steal a a sweater made of candy that he was planning on sneaking into a Fat Camp his parents were sending him to. He was also seen at the very end of Operation: Z.E.R.O., along with countless other operatives.

Numbuh 65.3 was last seen in Operation: T.R.E.A.T.Y., among the KND operatives firing blindly in the dark after the teens cut the power to the Moonbase and left a message for Numbuh 362.