The Rat King appeared in the 2012 Teenage Mutant Ninja Turtles cartoon, voiced by Jeffrey Combs.
In this series, the Rat King was introduced as Victor Falco, a scientist working on a neurochemical that allows him to read thoughts, and ultimately, to anticipate every move the Turtles make. He first appeared in "Monkey Brains," where the Turtles discovered that Falco had been experimenting on his partner, Dr. Tyler Rockwell, and turned him into a humanoid mutant chimpanzee that can read emotions, with Donatello defeating him in a fight by utilizing Splinter's earlier lessons about how to avoid thinking in a fight. In "I, Monster," Falco went into hiding, but continued his research in a rat-infested lab. Rats gnawed through electrical wire, causing the wires to fall into the neurochemical and trigger an explosive chemical reaction. The explosion left Falco disfigured, but it gained him telepathic control over rats. Now gaunt and corpse-like, Falco dubbed himself The Rat King and tried to use his new psychic abilities to manipulate Splinter into fighting and killing his own mutated turtle sons, but Splinter eventually shook off the mind control and defeated Rat King, whose unconscious body was carried away by his rats. In "Of Rats and Men," Falco used his access to Splinter's mind to learn more about the mutagen and attempted to create an army of mutant rats that he can control. Despite his increasing control of Splinter as he used him to attack the Turtles, Splinter continued to resist Rat King's control, which was broken when Michelangelo threw his "ice cream kitty" at him, attacking him and breaking his control over Splinter. With Rat King's mutation having to have cost him his sight, he was reliant on his rats to see for him, which allowed him to see through Splinter's eyes during his fight, as well as the rat on his shoulder, which he named "Aristotle". Splinter was able to gain the upper hand by knocking Aristotle away and then donning a blindfold so that he can fight Rat King without Rat King being able to see him in return. The fight concluded with Rat King attempting to charge at Splinter, only to fall off a high ledge in the sewers, possibly killing him.