Bradley the Skunk, aka Numbuh 6, aka R.O.B.O.-B.R.A.D.L.E.Y. is a baby striped skunk that was discovered and adopted by Numbuhs 2 and 3 in Operation: C.A.M.P. with Numbuh 5 serving as Bradley's Godmother. During the preparation for a mission to Camp Lemme outta here, the members of Sector V were preoccupied by their new pet, much to the disdain of Numbuh 1. However, when the mission is carried out, Bradley saves the day by awakening Chester's brainwashed campers with his spray. Bradley is then made an honorary member of the Kids Next Door and dubbed "Numbuh 6".
In Operation: H.O.S.P.I.T.A.L., Numbuh 6 was hit by a car and mortally injured, while on an undercover mission to spy on Numbuh 5's older sister, Cree Lincoln. He was sent to a hospital which, by chance, was the base of Cree's current operations. When a team of surgeons failed to save his life, Numbuhs 2 and 3 saved Bradley's life by turning him into a cyborg or, as Numbuh 2 puts it, "a half skunk, half KND operative, half butt-kicking machine", R.O.B.O.-B.R.A.D.L.E.Y, who proceeded to defeat Cree in a one-sided battle.
Numbuh 6 also appears in Operation: S.I.X., in which he joins Numbuh 3 and Numbuh 2 on their supposed soda smuggling mission.