Regarding the suggestions of Alexander and Caesar, I hate them both. Men who bring empire-building usually do not earn my respect. Caesar is my least favorite man in all of human history because he committed the single greatest sin: he killed a republic.
Jesus dude, where did you learn history? You sound like you studied under Dixie. The notion that Ceaser killed the Roman Republic tells me you just simply haven't studied much about the Republic. You need to go read Plutarch, Livy, Pliny.
Caesar did not kill the Roman Republic. The Republic collapsed due to it's own utter incompetency. If it had not been for Caesar it would have collapsed 40 years sooner then it did and it was Actually Octavian who put an end to the Republic, not Caesar.
The Roman Republic had become a corrupt oligarchy concerned about their own well fare and advancement and not the logistics of running a world wide Empire. The Decline of the Republic really dates back to the reforms of the brothers Grachii. It was actually the millitary reforms of Gauis Marius, though unintended, which undermined the Republic. Both he and Sulla employed large Armies who, because of the Senates ineptitude, were loyal to Marius and Sulla and not the Roman State. They set the precedent for the millitary and political events that eventually doomed the Republic. Caesar tried his damnedest to implement reforms that would have saved the Mos Maiorum and all of his reforms he contributed which could have saved the Republic (at least for a while). It was the Senate it self which gave Caesar his extra constitutional powers which were outside the mos maiorum and set the precedents which Octavian later used to end the Republic.
But that's a moot point anyways. The Republic had proven that an oligarchy designed and intended to manage the political and administrative affairs of a small city state were incapable of managing the affairs of a world wide empire the size of the Roman Empire.
Caesar even refers to this when he said, about Sulla's reforms, which were reactionary in the extreme and was intended to concentrate power in the old oligarchy and then retired, setting those reforms adrift, when he said that Sulla didn't know his political ABC's.
The facts are that Caesar was a universal genius who succeeded brilliantly in everything he did. From rising above humble origins, to his brilliance as a politician, to his genius as general who never lost a battle, to a brilliant author and writer of essay's and accounts. Caesar was one of the true great geniuses of human history and if you think he ended the Roman Republic, then you really don't know shit about the history of the Roman Republic.