Justin Cavallero (Numbuh 50) is one of Chad Dickson's friends who is also a member of The Teen Ninjas. He appears in Operation: E.L.E.C.T.I.O.N.S. with a speaking role: he tells Chad that the Gallagher Elementary students have no chance against their Hendry Middle School forces, and then they are both sent back to their seats (being in a classroom).
Later during the battle between both schools, he interrupts Chad as he's sweet-talking a girl with news that they might have a problem defeating the elementary kids. Then he is told to ready Chad's bike - and not to "scratch it or nothing".
He also appears in Operation: T.R.E.A.T.Y. when Chad and Numbuh 1 are in a Teen hangout undrneath a mini-mart. He reminds Chad that no kids are allowed to know about their hangouts, so he and several other Teen Ninjas chase him out. They intend to shoot him out of the sky; when Kids Next Door aviators tell him to stand down because they're in a "no-fly zone", he tells them that the guys they're chasing (Chad and Numbuh 1) stole his little brother's bike. It is unclear whether or not this was a lie, or if he really does have a little brother.
After this, he makes no further appearances, and his voice is unknown.