Gaius Julius Caesar (100–44 BC) is a military general and statesman who played a critical role in the events that led to the demise of the Roman Republic and the rise of the Roman Empire. A member of the Julian gens, Caesar displayed military genius in the Gallic Wars, where his campaigns brought Gaul under Roman control. His crossing of the Rubicon River in 49 BC, defying the Senate's authority, led to civil war, out of which Caesar emerged as the unrivalled leader of Rome. Declared dictator perpetuo (dictator in perpetuity), his centralisation of power and ambitious reforms aimed at addressing Rome’s numerous issues but also ignited concerns regarding his monarchical intentions. Notably, he introduced the Julian calendar, which is the basis of the calendar used today. Fearing his growing power, a group of senators, including his friend Brutus, assassinated him in 44 BC. His death catalysed the end of the Roman Republic, paving the way for the ascension of his grandnephew, Augustus, as the first Roman Emperor, and thereby the establishment of the Roman Empire.