Short answers, pulled from the story.
Plato invented Atlantis as a fictional island in his dialogues Timaeus, written in 360 BC, and Critias. Present-day philologists and classicists agree the story is fictional. Aristotle, who was Plato's own student, believed Plato had invented the island to teach philosophy.
Plato placed Atlantis beyond the Pillars of Hercules in the Atlantic Ocean, describing it as an island larger than Libya and Asia Minor combined. Some scholars have argued that the Pillars of Hercules in Plato's account referred to mountains on either side of the Gulf of Laconia in Greece rather than the Strait of Gibraltar.
Ignatius L. Donnelly published Atlantis: The Antediluvian World in 1882, arguing that all known ancient civilizations descended from a technologically advanced Atlantis and that the Biblical Garden of Eden was located there. He is credited as the father of the nineteenth-century Atlantis revival and popularized the idea that myths contain hidden historical information.
The ariosophic movement in Germany around 1900, propagated by figures such as Guido von List, reinterpreted Atlantis as the homeland of a Nordic-Atlantean master race. Alfred Rosenberg incorporated this into The Myth of the Twentieth Century in 1930, and SS-leader Heinrich Himmler made it part of official Nazi doctrine.
Viktor Ullmann composed Der Kaiser von Atlantis, with a libretto by Petr Kien, in 1943 while both were inmates at Theresienstadt. The Nazis banned its performance, recognizing the Emperor of Atlantis as a satirical figure for Hitler. Both composers were murdered in Auschwitz; the manuscript survived and premiered in Amsterdam in 1975.
Helena Petrovna Blavatsky, founder of the Theosophists, wrote about Atlantis in The Secret Doctrine in 1888, claiming the book was originally dictated in Atlantis. She described the Atlanteans as the fourth root race in a scheme of racial evolution, succeeded by what she called the Aryan race, and placed the peak of Atlantean civilization between one million and 900,000 years ago.