What person who died young would have changed history the most had they lived longer?

The younger Crasuss (son of Julius Ceasar’s triunrivate colleague of the same name) was widely considered to rival Ceasar himself in both military and political skill, and be one of the few people how could sucessfully oppose him in the impending crisis. He was however killed with his father during an ill fated invasion of persia with his father, before this could be tested.