Jerry the Troll King is a one time character in the series, "Secret Mountain Fort Awesome." He rules over a magical land where the music never stops and everyone dances (though he seems to be the only one that does so). His sole appearance is in the Season 2 episode, "Labyrinth."
Jerry is a slender man with knobby elbows and knees and a long nose. He has spiky shoulder length blonde hair with no visible ears. He also has bony claw like hands and a curved chin. He is dressed in Renaissance-style attire complete with a red cape, a gold broach with a ruby, frilly shoulder pads, a blue top, a black belt with a gold buckle, striped green pants with blue leggings, and long white boots with curled toes. His overall appearance, voice, and mannerisms are meant to mirror those of Jareth the Goblin King from the 1986 film "Labyrinth."
Jerry is a persuasive and cunning man who wants people to join him in his "magical land of whimsy where you dance until the music stops which is never." He likes people to be honest with their wishes to the point that he hits the roof when Gweelok says his wish was figurative and not literal (even though he specifically used the word "literally" when he made the wish).
He is also quite seductive as evidenced in the "Let's Dance Together" musical number, and has a relatively friendly demeanor overall. Jerry also has a sadistic side which is revealed both when he tortures the other Disgustoids with the "Happy Dance" musical number, and when he sends the Jester Guy to his death on the dance floor to demonstrate what happens when you try to walk on it.