Numbuh 30c was an operative, supposedly from an Arctic sector, who joined Sector V in Operation: A.R.C.T.I.C. on their mission to stop Professor XXXL's plan to eliminate school snow days. He is initially seen wearing a heavy coat, goggles and scarf that conceal his entire body. Later, 30c reveals that he is working for XXXL and betrays the KND, taking off his snowsuit to reveal a hot weather-oriented Hawaiian-style outfit. He then explains that 30 degrees Celsius is equivalent to about 80 degrees Fahrenheit, which was an indicator of his true nature. Shortly after this, it is revealed that Professor XXXL is not actually the one creating the weather control device, and was actually working on creating the perfect snowcone, and that while Numbuh 30c did deceive and betray the KND, he was not involved with the plot to eliminate snow days. Much later, in Operation: S.C.I.E.N.C.E., he appeared along with his team, Sector H, at the 2x4 Technology Convention, where they made a snow machine, but to use it you need to use a lot of items. He has a crush on Numbuh 3 and said she was cute which made Numbuh 4 jealous.
Numbuh 30c very closely resembles Kenny from "Kenny and the Chimp", although his face is not seen even without his extra clothing. This is reinforced by his association with Professor XXXL and both being voiced by Tom Kenny. It very likely they are the same guy.
He is the first KND Operative whose code name breaks away from the normal number sequence, adding the letter C to it.
His codename being a dead givaway for his betrayal was actually a mistake they worked into the episode.