Diocletian became emperor by a stroke of luck. He was losing a battle with the emperor Carinus, when several of Carinus’ officers, offended with his seducing of their wives, took revenge and killed him. Immediately they recognized Diocletian as their true emperor.
He was a strong leader who deserves first rank in the history of the empire, but also suffers from a bad reputation fostered by Christian writers who curse him for his persecution of their people.