The Rat King is the name of a large cluster of rats, first seen in "Chapter 6: The Nightmare Spirit". They only appear in the animated series.
The dozens of rats that make the Rat King are tied together with their tails. All of these rats are capable of human speech, and have human level intelligence. They share a single consciousness and always speak in perfect union, but still still refer to themselves in the plural ("we"). They have glowing, red eyes and move around by rolling around the ground in a large ball.
According to Hilda's Book of Beasts and Spirits, the Rat King came to be when at some point in Trolbergs history, dozens of the rats racing around in the sewers became hopelessly tangled together with their tails. Over time, they came to speak, think and act as one.
The Rat King is the keeper of all secrets of the people in Trolberg. They get most of these secrets from the rats that overheard them, or by trading them with others. The Rat King is an ally of the Marra, and they frequently exchange secrets, but the king is not afraid to reveal secrets about them if they can get something for it in return.
When Hilda, David and Frida visited the Rat King in the sewers, they revealed to Hilda that a Marra was responsible for David's nightmares in return for Hilda telling them her secret; that she's afraid of riding a bike and doesn't want her friends to find out. The Rat King later gave this secret to the Marra, who used it against Hilda to give the girl a nightmare.
In "The Draugen", Hilda seeks out the Rat King again to learn any secrets about Erik Ahlberg. The Rat King first wants a fried cod sandwich from the Salty Maiden; one that has aged in the dumpster outside. Hilda is eventually able to get them this sandwhich, but it turns out the Rat King was unable to dig up any dirt on Erik Ahlberg.
In other media
- In the graphic novel Hilda and the Bird Parade, when Hilda and The Great Raven are wandering around the harbor, they see a shadow of what appears to be the Rat King, and flee. But it turns out to be just 3 white mice. This scene was not included in the animated adaptation. The real Rat King does not appear in any of the graphic novels, leaving it unclear if the creature actually exists in this continuity.
- In the Hilda Tie-In Series, the Rat King is only briefly mentioned once in "Hilda and the Nowhere Space" in one of the scary campfire songs from the Sparrow Scouts.