The Roman general responsible for the expansion of the Roman Republic through conquest was Julius Caesar. Known for his military genius, Caesar played a crucial role in the conquest of regions like Gaul, expanding Roman territory significantly. His successful campaigns transformed him into a powerful figure in Roman politics, which ultimately led to his appointment as dictator for life. Caesar's actions sparked a series of civil wars, culminating in the end of the Republic and the rise of the Roman Empire. His legacy includes significant reforms in governance, military strategy, and the calendar, which still bears his name.