|Sector||Deep Sea Science Lab, temporary|
|Occupation||Kids Next Door Scientist, Splinter Cell Member|
|Appearances|| Operation: F.E.R.A.L.|
|Cameos|| Operation: I.T.|
He first appeared in Operation: F.E.R.A.L., where he and Numbuh 71.562 try to cure an ape-ified Numbuh 1 and get into an argument about whether to use "Element L", which Numbuh 74.239 believes might cause him to remain feral forever. In this episode, it is stated that he is in the 4th grade while Numbuh 71.562 (see in other operatives) is in the 5th grade.
Numbuh 74.239 is a recurring KND scientist who is later revealed to be a member of the KND Splinter Cell. He is voiced by Dave Wittenberg.
Numbuh 74.239 later appears in Operation: V.I.R.U.S., Operation: P.L.A.N.E.T., Operation: O.U.T.B.R.E.A.K., Operation: Z.E.R.O., Operation: I.T., Operation: S.C.I.E.N.C.E. and Operation: T.R.E.A.T.Y.. In which he is revealed to be in splinter cell, talking to Numbuh Infinity with a voice changer at the end of the episode. In the series finale, Operation: I.N.T.E.R.V.I.E.W.S., he is again revealed to be part of the KND Splinter Cell, which itself is a cover group for the Galactic KND. It is he who tells Numbuh 1 that he was selected to join the Galactic KND and fight the alleged "disease" of adulthood. In an earlier scene, he makes Father release Sector V by threatening to destroy his cake.
He also made a cameo in The Grim Adventures of the KND. When Mandy's M.A.N.D.R.O.B.O.T. shoots mustard instead of the supposed-to-be laser, it was revealed that the laser was sent to a KND Bratwurst Factory (Numbuh 74.239 is seen exclaiming, "Say, this laser cuts through bratwurst pretty nicely!")