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Asimov fleshes-out the character's origins in Prelude to Foundation (1988). Amaryl was born on Trantor in the Dahl sector. He worked as a "heatsinker", one of many people tending the vast subterranean operations that generate energy from heat in the deep recesses of the planet. The work was hard, hot and did not require great intelligence. These menial workers tended to be ostracized by those not forced to work underground.
Amaryl managed to discover and study mathematics with the help of a friendly librarian. He met Seldon when the latter visited the heatsink complex out of curiosity whilst fleeing from Eto Demerzel and living in Dahl. Seldon immediately recognized and fostered Amaryl's innate mathematical abilities and was able to get him into University. He eventually gained a doctorate and became Seldon's closest and most trusted co-worker. Amaryl's devotion to his work would be his undoing, giving him an early death from overwork.
Yugo Amaryl…..Physicist and Mathematician. He is in the position after Seldon in his Psychohistorical contribution for Future Developments. Himself…… He started his life dramatically in Dahl Sector more than his contribution in Psychohistory. He had born in extremely poor in Dahl Sector of Trantor. His life may pass as a very simple person, if unfortunately he did not meet with Hari Seldon………
In Forward the Foundation, Amaryl is the one to discover Wanda Seldon's mentalic powers, when Wanda reads his mind. On his deathbed, Amaryl tells Seldon about this incident and urges Seldon to follow up on it. Just before death, Amaryl then conceives of a large group of mentalics keeping humanity on the original track of psychohistory; this idea would come to fruition as the Second Foundation.