Gaius Julius Caesar , July 13, 100 BC – March 15, 44 BC), was a Roman military and political leader. He played a critical role in the transformation of the Roman Republic into the Roman Empire.
A politician of the populares tradition, he formed an unofficial triumvirate with Marcus Licinius Crassus and Gnaeus Pompeius Magnus which dominated Roman politics for several years, opposed in the Roman Senate by optimates like Marcus Porcius Cato and Marcus Calpurnius Bibulus. His conquest of Gaul extended the Roman world all the way to the Atlantic Ocean, and he also conducted the first Roman invasion of Britain in 55 BC; the collapse of the triumvirate, however, led to a stand-off with Pompey and the Senate. Leading his legions across the Rubicon, Caesar began a civil war in 49 BC from which he became the undisputed master of the Roman world.