Erich von Däniken, the Swiss author whose bestselling books about the extraterrestrial origins of ancient civilizations won him fame among paranormal enthusiasts and scorn from the scientific community, has died. He was 90.

His representatives announced on his website on Sunday that he died the previous day in a hospital in central Switzerland.

Von Däniken rose to prominence in 1968 with his first book, Chariots of the Gods, which claimed that ancient civilizations such as the Mayans and Egyptians were visited by alien astronauts who imparted advanced technology, enabling them to build monumental structures like pyramids.

The book tapped into growing public interest in unexplained phenomena at a time when conventional science was on the brink of sending humans to the Moon.

More than two dozen similar books followed, creating a literary niche that blended fact and fantasy. Swiss public broadcaster SRF reported that nearly 70 million copies of his books were sold in more than 30 languages, making him one of Switzerland’s most widely read authors.

Although von Däniken brushed off criticism, his life was marked by recurring financial troubles. Born in 1935 in Schaffhausen to a clothing manufacturer, he reportedly rebelled against his father’s strict Catholicism and the priests who taught him at boarding school, developing alternative explanations for the origins of life.

After leaving school in 1954, he worked as a waiter and bartender and was repeatedly accused of fraud, serving several short prison sentences. In 1964, he became manager of a hotel in Davos and began writing Chariots of the Gods. Its rapid success was soon followed by further convictions for tax evasion and financial impropriety.

By the time he left prison, the book was earning him a fortune, and a second work, Gods from Outer Space, allowed him to devote himself fully to his paranormal pursuits and worldwide travels.

During the 1970s, von Däniken undertook numerous trips to Egypt, India, and particularly Latin America, whose ancient cultures fascinated the amateur archaeologist. He lectured extensively, founded societies to promote his ideas, and later pioneered the use of video and multimedia to reach larger audiences.

In 1991, he became the first recipient of the “Ig Nobel” Prize for Literature, awarded for raising public awareness of science through questionable claims.

In 1985, he published New Memories of the Future, responding to critics by insisting that none of his core theories had been disproved. While his popularity declined in the English-speaking world by the 1980s, his work influenced popular culture, including television shows such as The X-Files.

Von Däniken is survived by his wife of 65 years, Elisabeth Skaja, a daughter, Cornelia, and two grandchildren.