The date of harmonic convergence was created by Tony Shearer, an author of Lakota heritage who was studying the culture and myths of ancient Mexico. His ideas were first published in 1975 in his book Beneath The Moon and Under The Sun. He believed that the period between the arrival of the conquistador Cortez, reputedly on Easter Sunday, April 21, 1519, and August 16, 1987, corresponded to a prophecy attributed to the visionary leader known as Ce Acatl Quetzalcoatl.