The strip was first called Little Nemo in Slumberland and then In the Land of Wonderful Dreams when it changed papers. A brief revival of the original title occurred from 1924-27.
Although a comic strip, it was far from a simple children's fantasy; it was often dark, surreal, threatening, and even violent. The strip related the dreams of a little boy: Nemo (meaning "nobody" in Latin), the hero. The last panel in each strip was always one of Nemo waking up, usually in or near his bed, and often being scolded (or comforted) by one of the grownups of the household after crying out in his sleep and waking them. In the earliest strips, the dream event that woke him up would always be some mishap or disaster that seemed about to lead to serious injury or death, such as being crushed by giant mushrooms, being turned into a monkey, falling from a bridge being held up by "slaves", or gaining 90 years in age. The adventures leading to these disasters all had a common purpose: to get to Slumberland, where he had been summoned by King Morpheus, to be the "playmate" of his daughter, the Princess.
Sometime during early 1906, Nemo did indeed reach the gates of Slumberland, but had to go through about four months of troubles to reach the Princess. His problem was that he kept being awakened by Flip, who wore a hat with "Wake Up" written on it. One sight of Flip's hat was enough to take Nemo back to the land of the living during these early days. Although at first an enemy, Flip went on to become one of the recurring heroes. The others included: Dr. Pill, The Imp, the Candy Kid and Santa Claus as well as the Princess and King Morpheus.
The "Slumberland" of the title soon acquired a double meaning, referring not only to Morpheus's fairy kingdom, but to the state of sleep itself: Nemo would have dream-adventures in other imaginary lands, on the Moon and Mars, and in our own "real" world, made fantastic by the dream-state.
The strip was not a great popular success in its time. Most readers preferred the slapstick antics of such strips as Katzenjammer Kids, Happy Hooligan, and Buster Brown to the surreal fantasy of Nemo, and other comic strips like Krazy Kat. However, during the late 20th century and early 21st century, the strip received more recognition. Among the most noticeable of its qualities were its intricate visual style — often with high levels of background detail — its vivid colours, fast pace of movement from panel to panel and the huge variety of strange characters and scenery.
Certain episodes of the strip are particularly famous. Any list of these would have to include the Night of the Living Houses (said to be the first comic strip to enter the collection of the Louvre) where Nemo and a friend are chased down a city street by a gang of tenement houses on legs; the Walking Bed, where Nemo and Flip ride over the rooftops on the increasingly long limbs of Nemo's bed (see illustration); and the Befuddle Hall sequence, where Nemo and his friends attempt to find their way out of a funhouse environment of a Beaux Arts interior turned topsy-turvy. McCay's mastery of perspective, and the extreme elegance of his line work, make his visions graphically wondrous. The eccentric dialogue is delivered in a dreamy deadpan, and often appears to be hastily jammed into tiny word balloons that can scarcely contain it. A typical line: "Whoever named this place Befuddle Hall knew his business! I am certainly befuddled."
The strips, along with most of the rest of McCay's works, fell into the public domain in most of the world on January 1, 2005, 70 years after McCay's death (see Copyright and the EU's Directive harmonizing the term of copyright protection for details). All of the works published before 1923 are in the public domain in the United States. The complete set of Little Nemo strips is available in a single volume from Taschen: Little Nemo 1905-1914 (ISBN 3-8228-6300-9), leaving out only the later revival from the 1920s, which is still under copyright in the U.S.
110 of the most famous strips have been reprinted in their original size and colors in the 2005 collection Little Nemo in Slumberland, So Many Splendid Sundays , a 16x21 inch hardcover book from Sunday Press Books.