He works away on his latest book, answers fan mail, and at midday, reaches for his cane, floppy hat and overcoat, and rides the elevator down from the second floor to the lobby. The doorman hails him a cab for the $4 ride to a nearby diner, Cafe Eighty Two on Broadway, for the lunch special, the chicken gyro, where there are other elderly people doing the same.

Image To Zecharia Sitchin, a carving from 7,000 B.C. represents an alien passing a plow, and agricultural wisdom, to humanity. Credit... Chester Higgins Jr./The New York Times

The Upper West Side is Mr. Sitchin’s Mesopotamia, Broadway a fertile valley. He has Lincoln Center, Zabar’s, Fairway, dry cleaners that deliver and a galaxy of take-out restaurants. For research, the New York Public Library is down on 42nd Street, and the archives of the Jewish Theological Seminary up on Broadway at 122nd Street.

“In Florida, if you don’t have a car, you might as well lay down and die,” he said. “I’ve been all over the Western world and I know of no other place where an older person like myself can survive on his own. I raise my hand, and my chauffeured car  a yellow cab  takes me anywhere. I can call any restaurant or store and get what I need delivered in minutes.”

He slides over a cup of coffee in a mug with a 30th anniversary logo for “The Twelfth Planet,” his seminal first book, now in its 45th printing. It stated his basic theory, based largely on his reading of texts preserved on clay tablets from the pre-Babylonian era in ancient Mesopotamia, the so-called cradle of the civilization of Sumer.

Born in Russia and raised in Israel, Mr. Sitchin studied economics in London and worked as a journalist and editor in Israel before moving to New York in 1952. Here, he was an executive at a shipping company and, with his wife of 66 years (she died in 2007), raised two daughters. He spent his free time studying, leading archaeological tours to ancient sites and spreading his unusual gospel.

Starting in childhood, he has studied ancient Hebrew, Akkadian and Sumerian, the language of the ancient Mesopotamians, who brought you geometry, astronomy, the chariot and the lunar calendar. And in the etchings of Sumerian pre-cuneiform script  the oldest example of writing  are stories of creation and the cosmos that most consider myth and allegory, but that Mr. Sitchin takes literally.