The Rat King, aka Dr. Victor Falco, is a bright but ruthless scientist. Working with the Kraang, he develops a psychic ingredient which gives him powerful telepathy. He can read human and mutant minds—like those of the Turtles!
In a subsequent experiment, he transforms himself into a rat hybrid with the power to psychically control those numerous rodents. His goal is to take over New York City and gain control of Splinter's mind.