Of the Empire it was the Roman Senate which was headed by two Consuls who had a lot of power, but were elected by the senate. Later in Rome's history they had emperors starting with Gaius Julius Caesar who had become Emperor by winning a massive civil war against Mark Anthony. He was later killed by an assassination carried out by the senate, but in the end Rome was still ruled by Emperors which led to it's decline and ultimate collapse as most were poor leaders or often corrupt.
