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.
As a normal skunk, Bradley's only real abilities were his cuteness, and his skunk spray.
After being transformed into R.O.B.O.-B.R.A.D.L.E.Y. he gained enhanced vision and laser vision through his cybernetic eye. His natural skunk stink was made even stinkier by his cybernetics.
Numbuh 6 is the only operative that has a mechanical design, is a baby and is an animal (skunk). It's possible that between "Operation: C.A.M.P." and "Operation: H.O.S.P.I.T.A.L.", he attended KND Arctic training facility and graduated. Numbuh 6 is likely named after his voice actor, Dee Bradley Baker.