Dr. Victor Falco was a sleazy scientist who used his knowledge and talents for his own selfish gain. After an accident involving a fire, Mutagen, and a chemical he was developing o give him telepathic powers, he became this series' incarnation of Rat King.
Rat King started out as a human scientist named "Dr. Victor Falco", and he debuted in the episode Monkey Brains. He and his colleague Dr. Tyler Rockwell were working on an experiment that involved Mutagen, a neurochemical, and monkey DNA when they were approached by the Kraang. When it was mentioned on the news that Dr. Tyler Rockwell was missing, Dr. Falco alluded that he was oblivious to the situation.
Falco pretended to help April O'Neil and the Turtles - and gained their sincere trust. The Turtles later figured out what Dr. Falco was really doing; experimenting with mutagen on his former colleague, Dr. Tyler Rockwell, turning the latter into a mutant monkey with the mutagen. Falco gained the same psychic powers temporarily by extracting a neurochemical from the mutant's brain and injecting himself with it. With his new power, Falco was able to defeat the Turtles in combat by reading their thoughts and predicting their every move. Donatello finally defeated him by fighting without thinking, but Falco escaped before the Turtles could ask him what he knew about the Kraang.
In episode 13, I, Monster, Falco was shown living in hiding, and continued to work on his psychic neurochemical in a secret laboratory, with only sewer rats to experiment on. One day, the rats chewed through some cables and started a fire in the lab. Falco was injured by the flames, but the neurochemical splattered on him, granting him a psychic connection to rats. Falco used his new ability to control the rats in his lab and they saved him from the fire. Some time later, Falco went into hiding in the sewers, nicknamed himself as The Rat King, and began plotting to use his powers to take over New York City. He launched a full scale assault on the city with his hordes of rats. Eventually, Rat King became aware of Splinter through telepathy. Knowing that the Turtles would come to stop him, The Rat King used psychological warfare to control Splinter's mind. When Splinter fights the Turtles, they are overconfident because they were actually able to land a blow on him (though they lost soon after), but soon realize that Splinter was going easy on them all of those years. They manage to snap him out of it and Splinter defeats The Rat King with nothing but two fingers. Rat King was last seen being carried off by his rats. He is still alive...
Powers and Abilities
In "Monkey Brains", Falco (after gaining the neurochemical DNA from Rockwell and injecting it into his own mind), had the abiity to read minds and uses it to stop anyone. This is observed when he read the Turtles' thoughts and was able to defeat them in combat (except for Donatello, who was eventually able to defeat Falco without thinking at all).
Like previous versions of the character, Rat King has psychic control over rats, being able to precisely command single individuals and large swarms. His powers were even able to control Splinter's mind, but Splinter was able to fight it. Rat King also has bandages covering his eyes. However, it has been shown that his powers allow him to see through the eyes of rats, both negating the need for his own eyes and making any rat a potential spy...
- Victor Falco is extremely similar to the H.P. Lovecraft character Herbert West, who was portrayed by Falco's voice actor, Jeffrey Combs in the "Re-Animator" film series. West was a scientist who experimented with a green substance similar in appearance (but not in effect) to the Ooze. As Rat King, his appearance somewhat resembles the appearance of Scarecrow from The New Batman Adventures (1997), who Combs also voiced.
- The Rat King's outfit (long black coat and black wide-brimmed hat) is nearly identical to the standard outfit worn by medieval plague doctors. This is noteworthy in that the Bubonic plague was spread by fleas being carried by rats.
- Michelangelo was extremely annoyed that the Rat King nicknamed himself, as he's the one who usually comes up with the nicknames. He tried numerous alternatives (Lord Rattington, Count Ratula, Verminator, etc.) until he begrudgingly accepts it.
- Rat King is the name of a phenomena in which many rats get stuck together by their tails.
- The Rat King's giant rats from Of Rats and Men were named after roman emperors and his little white rat, who serves as a royal vizier, received the name of Aristotle, a greek philosofer.