In the book, Pebble in the Sky, a retired tailor is transported tens of thousands of years into the future, finding himself in a place he does not recognize, where people speak a language he does not recognize, and he is mistaken for a genius by a couple who take him in and offer him for an intellectual experiment.
They mistake him for a mentally deficient person, and they secretly offer him as a subject for an experimental procedure to increase his mental abilities. While walking down the street in Chicago, Joseph Schwartz, a retired tailor, is the unwitting victim of a nearby nuclear laboratory accident, by means of which he is instantaneously transported tens of thousands of years into the future (50,000 years, by one character's estimate, a figure later retconned by future Asimov works as a "mistake"). 
