AMARYL, YUGO—… A mathematician who, next to Hari Seldon himself, may be considered most responsible for working out the details of psychohistory. It was he who …

… Yet the conditions under which he began life are almost more dramatic than his mathematical accomplishments. Born into the hopeless poverty of the lower classes of Dahl, a sector of ancient Trantor, he might have passed his life in utter obscurity were it not for the fact that Seldon, quite by accident, encountered him in the course of …

ENCYCLOPEDIA GALACTICA