He wanted to be greater than Alexander, and at the same age that Alexander had been at his peak, Caesar was stuck in a backwater province in Spain. He made a grand recovery though, eventually conquering western Europe, and was heading east to conquer Alexander's old empire when he was assassinated. And so he became greater than Alexander, modern rulers giving themselves the title Caesar (Kaiser of Germany, Czar of Russia) rather than Alexander, though some of the Czars also were christened Alexander just to have the best of both titles.