King Cake is the king of Birthday Cake Island. He is merely a lifeless piece of cake, with a crown, but he is still unanimously recognized as the ruler of all of Birthday Cake Island and the Clowns who live there.
In "Birthday Cake Island", Luc and Theo went to Birthday Cake Island to celebrate Luc's birthday. Shortly after being introduced to the king, Luc thought it'd be a good idea to eat him. The clowns were shocked and infuriated about the regicide of their beloved king, and they threatened to throw Luc and Theo into the volcano. Luc made up for it, by replacing the king with his real birthday cake and calling it "King Cake 2", which appeased the clowns, but when Jolly Pops translated the word of their second king, he said the damage had already been done and they continued on with Luc and Theo's punishment.
In "Rocket to Tomorrow", Claire crash landed a rocket, carrying herself, Luc, Theo, and Turk Parfait, into Birthday Cake Island, landing right on top of King Cake. The quartet was again thrown into the boiling volcano.