Planet of the Damned by Harry Harrison

Once in a generation, a man is born with a heightened sense of empathy. Brion Brandd used this gift to win the Twenties, an annual physical and mental competition among the best and smartest people on Anvhar. But scarcely able to enjoy his victory, Brandd is swept off to the hellish planet Dis where he must use his heightened sense of empathy to help avert a global nuclear holocaust by negotiating with the blockading fleet, traversing the Disan underworld, and cracking the mystery of the savagely ruthless magter. Summary by Great Plains.