The Nome King is an old enemy of the characters of L. Frank Baum's Oz books. His name was originally Roquat the Red. Although the Wicked Witch of the West is the most famous of the land of Oz's villians (thanks to the popular 1939 film The Wizard of Oz), the Nome King is the closest the book series has to a main antagonist, as he appears again and again to cause trouble for the Land of Oz on a regular, almost episodic basis.
In his first encounter with his enemies, Ozma of Oz, along with Dorothy Gale, the Scarecrow, the Tin Woodsman, and the Cowardly Lion conquered him and freed his slaves, the royal family of Ev, and took away his magic belt. He was so angry that he plotted revenge, building a tunnel under the deadly desert, and allying with a host of evil spirits to destroy the land and kill the people. Fortunately, he drank of the Water of Oblivion and forgot all, including his enmity and his name. Hereafter, he would be known as Ruggedo.
However, he learnt the old evil ways again after Ozma sent him home, and he enslaved the Shaggy Man's brother. Shaggy, with the help of Betsy Bobbin, Queen Ann of Oogaboo and her army, as well as some of Dorothy's old friends, invade and conquer the Nome King again, and force him into exile. After this, his former henchman, Kaliko is made the new king, but he promises to keep the ex-king if he behaves. However, Ruggedo seems incapable of doing this, and he is eventually exiled. He meets Kiki Aru and plans to destroy Oz again, and gets into the country without Ozma's knowledge, creating havoc. However, he drinks of the Water of Oblivion again and to stop him ever going bad again, Ozma keeps him in the Emerald City. He soon turns bad again, and runs away with the Emerald City on his head, after his hair turns into spikes. The Wizard eventually turns him into a cactus, so that he can never make trouble again.