Swiss author Erich von Däniken, known for popularizing theories about ancient alien astronauts, has died at 90. His 1968 book "Chariots of the Gods?" proposed that ancient civilizations received advanced knowledge from extraterrestrials, enabling monumental constructions like the pyramids. Von Däniken's books sold millions worldwide, translated into numerous languages, but his ideas were widely criticized by scientists and academics as pseudoscience. Despite controversy and past legal issues, he maintained his theories throughout his career.