Mu is a lost continent introduced by Augustus Le Plongeon (1825–1908), who identified the "Land of Mu" with Atlantis. The name was subsequently identified with the hypothetical land of Lemuria by James Churchward (1851–1936), who asserted that it was located in the Pacific Ocean before its destruction.
History of the concept
Augustus Le Plongeon
The mythical idea of the "Land of Mu" first appeared in the works of the British-American antiquarian Augustus Le Plongeon (1825–1908), after his investigations of the Maya ruins in Yucatán. He claimed that he had translated the first copies of the Popol Vuh, the sacred book of the K'iche', from the ancient Mayan using Spanish. He claimed the civilization of Yucatán was older than those of Greece and Egypt, and told the story of an even older continent.
Le Plongeon got the name "Mu" from Charles Étienne Brasseur de Bourbourg, who, in 1864, mistranslated what was then called the Troano Codex (now called "Madrid Codex") using the de Landa alphabet. Brasseur believed that a word which he read as Mu referred to a land that had been submerged by a catastrophe. Le Plongeon identified this lost land with Atlantis and, following Ignatius Donnelly in Atlantis: The Antediluvian World (1882), identified it as a continent that had once existed in the Atlantic Ocean: