Dorsai! (Childe Cycle, #1)

aka The Genetic General
Throughout the Fourteen Worlds of humanity, no race is as feared and respected as the Dorsai. The ultimate warriors, they are known for their deadly rages, unbreakable honor, and fierce independence. No man rules the Dorsai, but their mastery of the art of war has made them the most valuable mercenaries in the known universe.

Donal Graeme is Dorsai, taller and harder than any ordinary man. But he is different as well, with talents that maze even his fellow Dorsai. And once he ventures out into the stars, the future will never be the same.