Short answers, pulled from the story.
The description of Atlantis appears in Plato's dialogue Critias, written in 360 BC. The narrative claims that 9,000 years before his lifetime a war took place between those outside the Pillars of Hercules at the Strait of Gibraltar and those who dwelt within them.
Aristotle believed that Plato, his teacher, had invented the island to teach philosophy. Other ancient historians and philosophers who believed in the existence of Atlantis were Strabo and Posidonius.
Ignatius L. Donnelly published Atlantis: the Antediluvian World in 1882. He was greatly inspired by early works in Mayanism and attempted to establish that all known ancient civilizations were descended from Atlantis.
Madame Blavatsky reported that the civilization of Atlantis reached its peak between 1,000,000 and 900,000 years ago but destroyed itself through internal warfare brought about by the dangerous use of psychic and supernatural powers of the inhabitants.
Edgar Cayce asserted that Atlantis would rise again in the 1960s sparking much popularity of the myth in that decade. There is also a Hall of Records beneath the Egyptian Sphinx which holds the historical texts of Atlantis according to his claims.
The opera Der Kaiser von Atlantis written in 1943 by Viktor Ullmann with libretto by Petr Kien while both were inmates at Theresienstadt concentration camp was never performed by Nazis who assumed it satirized Hitler. Though Ullmann and Kien were murdered in Auschwitz the manuscript survived and was performed for the first time in 1975 in Amsterdam.