The Newtralizer is a character that debuted in the 2012 Teenage Mutant Ninja Turtles TV series. He is an enemy of both the Turtles and the Kraang. He is an amalgam of characteristics of a rejected toy design for Playmates Toys by Ryan Brown and a character created by executive producer Ciro Nieli whilst in elementary school. Due to The Newtralizer's costume, he is likely a parody of Marvel's The Punisher with inspiration provided in part by Judge Dredd. The most obvious feature in this respect is the skull-like pattern on the Newtralizer's chest that resembles the emblem on the chest of the Punisher's costume.
The Newtralizer is a resident of Dimension X. He was captured by the Kraang after considerable effort and imprisoned in a secret prison facility on Earth because he had a tendency to devour every living thing he met - including the Kraang. In an attempt by Donatello, to free Kirby O'Neil, Newtralizer was also accidentally freed and he promptly goes on a rampage. The turtles ultimately manage to defeat him, but he survives and escapes from the lab and continued his hunt to rid this plant of the Kraang.
He was later detained in the Kraang prison. After Metalhead frees all of the mutants, he escapes from Kraang captivity once again.
The Newtralizer returns and teams up with Slash against Raph and Casey. It is shown that he had helped Slash escape from a Kraang prison, which is what lead to them working together. Newtralizer and Slash viciously assault numerous groups of Kraang and steal their supplies to create teleportation devices. Newtralizer then plots to take control of the Kraang's newest weapon to destroy them and anybody who gets in his way. He is able to get a hold of it and destroys the Kraang in the area and attempts to use it on the Turtles. Casey arrives and launches a puck with a bomb strapped to it into it. Despite the damage sustained to the teleportation device, Newtralizer is able to escape. Once the Turtles leave, the Newtralizer suddenly teleports back, infused with energy as if he has become stronger.
The Newtralizer will reappear in Season 5, as a promotional video shows him battling Karai and Leonardo.