|“||You think you can hide? I know exactly where you are.||„|
|~ The Nightmare King|
The Nightmare King is the ruler of the dreaded Nightmare Land and the main antagonist of Little Nemo: Adventures in Slumberland.
The origins and history of the Nightmare King are unknown, but he is apparently the embodiment of nightmares, he rules over Nightmare Land, a dark world which represents all the fear and darkness of the world's nightmares. At some point in the past, he was imprisoned beneath Slumberland by his enemy, King Morpheus, the king of Slumberland. He was locked behind a giant door which all residents of Slumberland were forbidden to open lest the evil king be set free again.
During the movie, Morpheus summons a young boy named Nemo to Slumberland to be his heir and playmate to his lonely daughter, Princess Camille. Nemo is a boy who suffers from constant nightmares and while his parents say the reason is because of his habit of sneaking pies late at night, it is strongly hinted several times that the Nightmare King may, in fact, be the one responsible for his endless nightmares.
When Nemo is brought to Slumberland, the Nightmare King is released after Nemo unlocked the door that Morpheus warned him not to open using a royal golden key. Nemo rushes back to Morpheus' palace in time for his coronation ceremony, where Nemo is handed the royal scepter, the only thing capable of defending Slumberland in the event of the Nightmare King's return. In the middle of a dance session between Morpheus and Professor Genius, the Nightmare King reaches the castle and steals Morpheus away. As the partygoers search for a scapegoat, Flip reveals Nemo to be responsible for the Nightmare King's escape.
Nemo awakens in his home, which floods with seawater and ejects him into the ocean. Genius discovers Nemo and tells him not to blame himself for all that has happened. When the two return to Slumberland, Flip reveals that he has a map to Nightmare Land, where Morpheus is currently being held. Nemo, Camille, and Flip set off in a tugboat in search of Morpheus.
They are soon sucked into a whirlpool and find themselves in the monster-infested Nightmare Land. The trio comes across a group of shapeshifting goblins who wish to aid in the quest to find Morpheus. The Nightmare King sends a flock of giant bats creatures to seize the rescue party. Nemo attempts to use the scepter, but once again awakens back in his bed. The goblins appear in Nemo's room and the group travels together to the Nightmare Castle within the Nightmare Land by flying through a hole in the sky called the "Gate of Wind".
At his castle, the Nightmare King is informed that Nemo has been terminated, but his giant manta ray soon informs him that Nemo is in the castle with the sceptor, enraged the Nightmare King absorbs his army due to their failiure. He then sucks Nemo and his friends into his lair where he demands possession of the scepter. When Nemo fails to reply, the King reveals the Professor, Princess Camille, and Flip whom he has imprisoned in giant reliquaries and begins to taunt the boy. When even this fails, he tops it off by imprisoning King Morpheus in a reliquary of his own right before Nemo's eyes.Nemo tries to save him but the Nightmare King has his giant sting ray try to kill him but Nemo soon destroys it with the scepter. He again asks Nemo to give him the sceptre because, after all, Nemo cannot even remember the words necessary to use it. Nemo refuses and valiantly uses the scepter to fight off the Nightmare King by destroying his hand. Now enraged, the Nightmare King tries to absorb Nemo and his friends and finish them for good. In a last desperate effort, Nemo just barely manages to say the full incantation to the scepter unleashing it's full power to destroy the Nightmare King once and for all, albiet at the cost of his own life, ending his evil reign along with Nemo's own nightmares.
Shortly afterwards, all the King's spells are lifted freeing everyone and Nemo is quickly revived by King Morpheus who forgives him for breaking his promise. Sometime later, Slumberland celebrates the fall of the Nightmare Kingdom. After which Nemo returns home and once more awakens in his room, this time peacefully, now forever free from his endless nightmares due to the Nightmare King's destruction.
The Nightmare King appears as the primary antagonist and final boss of both the 1990 Nintendo videogame Little Nemo: Dream Master and the 1990 Capcom arcade game Nemo. In both games, he sends both his army of fiendish denizens of the Nightmare Kingdom and evil boss monsters to invade Sumberland and to destroy Nemo but Nemo took on and beaten his minions and than defeated the Nightmare King himself.
- He was voiced by both Tarō Ishida in the Japanese adaption and Bill Martin in the English adaption. Martin also voices the Shredder in the original Teenage Mutant Ninja Turtles animated television series.
- The Nightmare King bares strong resemblance to Chernabog.
- He also slightly resembles Black Doom from Shadow the Hedgehog.
- The Nightmare King is similar to Lord Nightmare from Kirby's Adventure and Wizeman the Wicked from NiGHTS.
- His face slightly resembles the Hellhound from All Dogs Go to Heaven.