A number of villain characters seen in Codename: Kids Next Door were never properly introduced or named. As such, none of them ever had a major role in any episode, and were usually only seen at large gatherings of villains, first at Operation: M.O.V.I.E.
Unintroduced villains whose names have been confirmed by Tom Warburton:
- The Iguana is the most frequently seen of the unknown villains. He is a man with peach-fuzz wearing a green lizard suit and red shoes, and possibly named after the coloring artist of the KND series. He usually appears at large villain meetings, but never has any lines. He was first seen in Operation: M.O.V.I.E., at Mr. Boss's meeting in a hat and jacket at the movie theater (for some reason had fuzz on his chin instead of above his lip and the costume not covering his hands, which was changed in later episodes) and is seen talking with Sergeant Sensible. The Iguana's face is seen on one of Numbuh 1's monitors in Operation: C.O.L.L.E.G.E.
In Operation: C.H.O.C.O.L.A.T.E., he is seen in the KND Arctic Base prison, in between Crazy Old Cat Lady and Toiletnator and being visited by a large blonde woman. In Operation: M.A.C.A.R.R.O.N.I., he's waiting for Mr. Boss to return with the macaroni art with other villains sitting near Mr. Fizz and Toiletnator. He is at the Supervillain's Supermarket in Operation: M.U.N.C.H.I.E.S. He attacks the KND in Mr. Boss's submarine in Operation: C.A.N.Y.O.N., and is accidentally flushed by Toiletnator. Also seen on Numbuh 2's newspaper in Operation: C.L.O.W.N. and in jail next to Toiletnator once again in Operation: M.I.S.S.I.O.N.. In Operation: Z.E.R.O., the Iguana is first seen attacking the KND Museum, and is later present at Father's meeting, where he is turned into a Senior Citizombie by Grandfather when he was at the Moonbase Headquarters when Numbuh 60 turned into a Senior Citi-zombies.
- The Bright Idea is a villain who controls electricity and the second most frequent appearing. He has a thin mustache, wears a giant light bulb on his head, a bright yellow outfit, and blue gloves. Like Iguana, first appearing in Operation: M.O.V.I.E. being splattered with ice cream from the Candy Guy's cart. In Operation: A.F.L.O.A.T., he is seen along with the other villains chasing the Kids Next Door, who attempted to crash the villain barbecue. In Operation: A.W.A.R.D.S., he is seen near Destructo Dad shouting at Numbuh 5, disguised as a waiter running the catering cart. He is seen in audience of Chester's dream in Operation: U.T.O.P.I.A. Like Iguana, he is seen also Operation: Z.E.R.O. at the KND Museum behind Mr. Boss, posing and pretending to be an earwax statue. Whenever he appears, Nogoodnik is usually with him.
- Nogoodnik is a blond-haired villain with an yellow-orange outfit with the letters "NG" on it, a red-violet mask, and hammer-like hands. He is supposedly the modeled after Tom Warburton himself, along with Numbuh Eleventy Billion. Like the other two above, Nogoodnik is first seen in Operation: M.O.V.I.E. sitting next to Bright Idea and later seen near Knightbrace who shouts at the escaping Numbuh 4. In Operation: Z.E.R.O. he can be seen at Father's meeting near Toiletnator, Count Spankulot, some Ice Cream Men, and Candy Pirates. He usually appears in the same episodes that Bright Idea appears in.
Other Unnamed Villains
- The Sheep Costume from Sheep in the Big City
- A Man with a Pipe Shaped Head
- Fishbowl-Head Helmet
- A Villain with a Giant Brain and a Wind-Up Dial on it
- The Helmet Space Boy
- Blue and Yellow Costume Guy
- Triangle Cyan Costume Guy
- A Purple Costume Guy with the letter "P" on it
- A Moai Statue with Rabbit Ears (Play on words for Easter Island and the Easter Bunny)
- A Large Blue Clown with Glasses
- A Villain with a Large Smoking Pipe in his mouth
- A Villain with a Giant American Football Shaped Head