Yugo Amaryl was a mathematician and a heat-sinker from Dahl, and one of the four individuals that Hari Seldon met during The Flight while laying the foundations of psychohistory. Seldon first met Amaryl in the Trantorian sector of Dahl, where he was taking refuge after having his initial presentation about psychohistory at the Decennial Convention. At the time, Amaryl (who is described as being about a decade younger than Seldon) worked in the Dahlite heat-sinks, which are one of the main sources of energy for the Empire. Upper-class Dahlites, however, held much prejudice against those forced to work in the heatsinks, and the two classes barely intermingled. Amaryl, however, was able to impress Seldon with his mathematical abilities, and Seldon promised to help him receive a scholarship to a university once he was safe. He kept his promise, and indeed, Amaryl became his right-hand man, the only person in the universe other than Seldon who was truly and intimately acquainted with psychohistory. For many years Seldon and Amaryl worked the problem of psychohistory alone, before Seldon's appointment as First Minister could afford him the luxury of large groups of people and the latest technology working to solve the issues.
Although from Dahl, Amaryl does not have the characteristic Dahlite mustache, and hardly identifies with the sector. He is described as being cold and aloof, interested solely in psychohistory, and a has a fierce loyalty to Seldon. Seldon originally thought he was a creative force who would challenge him to think of psychohistory in new ways. Amaryl relies much on his own intuition when working mathematical problems. He is said to be uninterested in women, companionship, or other pleasures.