The gods come from above and travel to Earth, walking among the people.
Sitchin interprets the Sumerian myths as being factual accounts of alien beings from an extra planet in Earth's solar system that came to Earth 450,000 years ago to mine for gold and other rare minerals.
Sitchin also speculated that Pluto was originally a satellite of Saturn but Nibiru's gravity perturbed it, sending it to the outer Solar System and giving the body its peculiar orbital path, intersecting the orbit of Neptune.
According to Sitchin, Nibiru (called "the twelfth planet" because, Sitchin claimed, the Sumerians' gods-given conception of the Solar System counted all eight planets, plus Pluto, the Sun and the Moon) was the home of a technologically advanced human-like extraterrestrial race called the Anunnaki in Sumerian myth, who Sitchin states are called the Nephilim in Genesis.
Sitchin believes that fallout from nuclear weapons, used during a war between factions of the extraterrestrials, is the "evil wind" described in the Lament for Ur that destroyed Ur around 2000 BC. Since the release of his first book The 12th Planet in 1976, Sitchin has written seven other books as part of his Earth Chronicles series, as well as six other companion books.
Sitchin's books have sold millions of copies worldwide and have been published in more than 25 languages.
While working as an executive for a shipping company, he taught himself Sumerian cuneiform and visited several archaeological sites.
Similar to earlier authors such as Immanuel Velikovsky and Erich von Däniken, Sitchin advocated hypotheses in which extraterrestrial events supposedly played a significant role in ancient human history.
Sitchin's ideas have been rejected by scientists and academics, who dismiss his work as pseudoscience and pseudohistory.
His work has been criticized for flawed methodology and mistranslations of ancient texts as well as for incorrect astronomical and scientific claims.