Little Nemo: Adventures in Slumberland (released in Japan as simply and credited in some territories as Little Nemo) is a 1989 animated musical fantasy film directed by Masami Hata and William Hurtz. Based on the comic strip Little Nemo in Slumberland by Winsor McCay, the film went through a lengthy development process with a number of screenwriters. Ultimately, the screenplay was credited to Chris Columbus and Richard Outten; the storyline and art style differed from the original version. The original soundtrack was penned by the Academy Award-winning Sherman Brothers. The film features the English dub voices of Gabriel Damon, Mickey Rooney, René Auberjonois, Danny Mann, Bernard Erhard, Laura Mooney, William E. Martin, Alan Oppenheimer, Michael Bell, Sidney Miller, Neil Ross, and John Stephenson.

Even though it derived from an American comic strip, Little Nemo was animated by the Japanese company Tokyo Movie Shinsha and thus is often considered an anime film, although it was a joint production of Japanese and American animators and production companies.

The movie was infamous for being in development hell for much of the 1980s, with many people involved with the production at some point before dropping out. Some of those attached to the film worked at Disney, Lucasfilm, Warner Bros. Cartoons, and Studio Ghibli. Those who expressed interest or were involved at some stage included George Lucas, Chuck Jones, Ray Bradbury, Isao Takahata, Brad Bird, Jerry Rees, Chris Columbus, Ken Anderson, Frank Thomas, Oliver Johnston, Paul Julian, Osamu Dezaki, the Sherman Brothers (Richard M. Sherman and Robert B. Sherman), Hayao Miyazaki (who was working at TMS at the time), and Gary Kurtz.

The film was first released in Japan on July 15, 1989, by the Toho-Towa and in the United States on August 21, 1992, by the Hemdale Film Corporation for the dub. It received mixed reviews and was a box-office bomb, earning $11.4 million on a $35 million budget. However, it sold well on home video and has since become a cult film.

Plot A young boy named Nemo experiences a series of nightmares (including being pursued by a locomotive). Upon awakening the one day, he goes with his pet flying squirrel, Icarus to see a parade welcoming a traveling circus. However, Nemo is unable to see the circus since his parents are too busy to take him. That night, Nemo imitates sleepwalking in an attempt to sneak some pie away, which acts against a promise he had made earlier to his mother, who catches him in the act and makes him run back to his room empty-handed.

Upon falling asleep, Nemo is approached by figures from the circus parade. The circus organist introduces himself as Professor Genius and claims that they had been sent on a mission by King Morpheus, the king of a realm named Slumberland. The mission involves Nemo becoming the playmate of the princess, Camille. Although Nemo initially has reservations about interacting with a girl, he and Icarus decide to set off to fulfill his mission after being persuaded with a gift box of cookies from the princess.

Nemo is taken to Slumberland in a dirigible which he is allowed to drive, causing some chaos, and is introduced to King Morpheus. Morpheus reveals that he summoned Nemo to become his heir to the throne. Morpheus gives Nemo a golden key that opens every door in the kingdom and warns him of a door with a dragon insignia that must never be opened. Nemo is introduced to Princess Camille and the pair roam Slumberland together.

Afterward, Nemo meets the mischievous clown Flip who convinces him to ditch his prince lessons, and later angers a group of cops, forcing him and Nemo to hide out in a cave. There, Nemo discovers the door that Morpheus warned him not to open. Flip tempts Nemo into unlocking the door, which unleashes "the nightmare". Nemo rushes back to Morpheus' castle in time for his coronation ceremony where he is handed the royal scepter, the only thing capable of defeating the Nightmare King, the ruler of Nightmare Land, should he ever return to Slumberland. In the middle of a dance session between Morpheus and Genius, "The Nightmare" reaches the castle and steals Morpheus away. As the partygoers search for a scapegoat, Flip and Nemo accuse each other, though the responsibility goes to Nemo who had the key.

Nemo awakens in his home, which floods with seawater and ejects him and Icarus into the ocean. Genius discovers them and tells Nemo not to blame himself for Morpheus's capture and that Flip is at fault for tempting him, but Nemo accepts his role in the situation, and pledges to find the King. When the three return to Slumberland, they rescue Flip from being shot out of a cannon into outer space because he withheld information on owning a map of Nightmare Land where Morpheus is currently being held.

Nemo, Icarus, Camille, Flip, and Genius set off in a tugboat in search of Morpheus. They are soon sucked into a whirlpool and find themselves in the goblin-infested Nightmare Land. The five come across a group of shapeshifting goblins called Boomps consisting of Oompa, Oomp, Oompe, and Oompy. They wish to aid in the quest to rescue Morpheus. The Nightmare King sends a flock of gigantic bats to seize the rescue party. Nemo attempts to use the scepter, but cannot remember the full incantation, and awakens in his bed along with Icarus again after watching Camille, Flip, and Genius get captured.

The Boomps appear in Nemo's room after he awakes. After reuniting with a lost member of theirs named Oompo who gives Nemo a letter from Morpheus containing the full scepter incantation, the group travels to Nightmare Castle by flying through a portal in the sky. However, they are subsequently trapped in the castle where the Nightmare King demands possession of the scepter, threatening his captives, including Morpheus, to try and force Nemo's compliance. After a fierce battle, Nemo uses the scepter to finally destroy the Nightmare King and purify Nightmare Land, but seemingly at the cost of his own life as well.

As everyone mourns Nemo's death, Morpheus uses the scepter to revive him, and accepts his apology for causing everything, assuring Nemo that his courage has allowed him to make up for his mistake and become a true prince. As Slumberland celebrates the fall of the Nightmare Kingdom, Camille escorts Nemo and Icarus home on the dirigible. She and Nemo then almost share a kiss.

Nemo awakens in his room, where he apologizes to his mother for breaking his promise and trying to take the pie. Nemo's parents also agree to take Nemo to the circus. Nemo stares out the window with Icarus as he looks forward to his new day.

Cast Gabriel Damon (Takuma Gōno in the Japanese adaptation) as Nemo, a human boy living in New York City who is taken to Slumberland to be the official playmate of Princess Camille. In actuality, he is being summoned to be the heir to the elderly King Morpheus. Mickey Rooney (Chikao Ōtsuka in the Japanese adaptation) as Flip, a clown who is described as a "frightful fellow" by Professor Genius, he is wanted throughout Slumberland for "having fun". He tricks Nemo into accidentally releasing the Nightmare King and blames Nemo for the ruin of Slumberland. In the real world, he is a clown in a circus that stops in Nemo's town. René Auberjonois (Kōichi Kitamura in the Japanese adaptation) as Professor Genius, King Morpheus' advisor. He comes to the real world to bring Nemo to Slumberland. In the real world, he is an organ player in a circus that stops in Nemo's town. Danny Mann as Icarus, a flying squirrel who is Nemo's best friend. He detests being called a "little rat" (which Princess Camille mistakes him for). His initial relationship with Princess Camille, though rough, eventually changes for the better. Bernard Erhard (Kenji Utsumi in the Japanese adaptation) as King Morpheus, the sovereign of Slumberland. He has protected Slumberland for years with the help of the royal scepter: an ancient weapon of great power. In the real world, he is the ringmaster of a circus that stops in Nemo's town. William E. Martin (Tarō Ishida in the Japanese adaptation) as the Nightmare King, a demonic horned creature who rules over the realm of nightmares. Laura Mooney (Hiroko Kasahara in the Japanese adaptation) as Princess Camille, the daughter of King Morpheus. Though she initially acts somewhat spoiled, she eventually grows to like Nemo. In the real world, she is riding on an elephant in a circus that stops in Nemo's town. Camille was modeled after Leah Allers and TMS wrote her a two-page thank-you letter. Greg Burson (Tesshō Genda in the Japanese adaptation) as Nemo's father Greg Burson as Flap, Flip's bird companion. Jennifer Darling (Mari Yokoo in the Japanese adaptation) as Nemo's mother Neil Ross (Hiroshi Ōtake in the Japanese adaptation) as Oompa, a member of the Boomps that befriend Nemo. Alan Oppenheimer (Keiichi Nanba in the Japanese adaptation) as Oomp, a member of the Boomps that befriend Nemo. John Stephenson (Masaharu Satō in the Japanese adaptation) as Oompo, a member of the Boomps that befriend Nemo and is the largest of the Boomps. Sidney Miller (Kōzō Shioya in the Japanese adaptation) as Oompe, a member of the Boomps that befriend Nemo. Michael Bell (Hiroko Emori in the Japanese adaptation) as Oompy, a member of the Boomps that befriend Nemo. Kathleen Freeman (Kimie Nakajima in the Japanese adaptation) as the dance teacher Bever-Leigh Banfield (Seiko Nakao in the Japanese adaptation) as the woman John Stephenson (Kazumi Tanaka in the Japanese adaptation) as the dirigible captain Bert Kramer (Yukimasa Kishino in the Japanese adaptation) as a goblin, a hideous creature that serves as a member of the Nightmare King's army. Beau Weaver (Tarō Arakawa in the Japanese adaptation) as a police officer Sherry Lynn as Bon Bon, a Page in Slumberland who works for King Morpheus. In the real world, he and his fellow pages are the drivers of the wagon with the organ in a circus that stops in Nemo's town. Guy Christopher as a Courtier and a police officer Nancy Cartwright and Ellen Gerstell as the pages, servants of King Morpheus. In the real world, they and Bon-Bon are the drivers of the wagon with the organ in a circus that stops in Nemo's town. Tress MacNeille as an elevator creature Michael McConnohie as an etiquette master Michael Gough as a teacher Michael Sheehan as a fencing master June Foray as the librarian Gregg Berger as the equestrian master

Production Nemo was the brainchild of producer Yutaka Fujioka, then president of Tokyo Movie Shinsha (TMS). He had long realized the limitations of the animation business in Japan and wanted to enter the U.S. market, so he started a new animation studio and planned to distribute U.S.-Japan co-produced animation films worldwide. He founded Telecom Animation Film in 1975, and embarked on a film adaptation of the legendary comic strip Little Nemo, which was so well known in the U.S. that two film adaptations were proposed during Walt Disney's lifetime. As the first step towards realizing this project, in 1977 he personally flew to Monterey, California, to convince the McCay descendants to allow him to obtain the film rights, and he finally won it in the summer of 1978.

Fujioka had another dream: to make a "full animation" (not Japanese limited animation) film that could compete with Disney. For this purpose, Fujioka hired newcomers with no experience in Japanese TV animation and had them trained by Sadao Tsukioka, followed by Yasuo Ōtsuka. Incidentally, the 1980 pilot film was created by Tsukioka.