Julius Caesar was the Roman leader known for his pivotal role during the fall of the Roman Republic. His crossing of the Rubicon River in 49 BCE initiated a civil war, ultimately leading to the end of the Republic and the rise of the Roman Empire. Caesar's accumulation of power and reforms, including centralizing the government and extending citizenship, sparked significant political conflict. His assassination in 44 BCE was partly a reaction to fears of his growing influence, which intensified the struggle between supporters of republican governance and those favoring autocratic rule. This period marked a transformative phase in Roman history.