Final answer:
While Julius Caesar's rise and actions were significant in the transition from Republic to Empire, it was Octavian, or Augustus Caesar, who institutionalized the shift. He reformed the political system, claiming to restore the Republic but establishing an imperial rule that would endure for centuries.
Step-by-step explanation:
The transformation from the Roman Republic to the Roman Empire was a complex process, not solely dependent on Julius Caesar's actions. Caesar's rise signaled underlying issues in Roman politics and society. He exploited opportunities to increase his power and influence, which in conjunction with his military achievements, made him immensely powerful and feared. Nevertheless, it was Octavian, later known as Augustus Caesar, who deliberately engineered a new political system, claiming to restore the Republic while actually establishing a hereditary empire. By the end of his rule, the hallmarks of the Roman Republic had been replaced, laying the foundation for centuries of imperial rule. Hence, while Caesar's role was pivotal, other forces and individuals also significantly contributed to the establishment of the Roman Empire.
After Caesar's assassination, a period of civil wars ensued, culminating in Octavian's rise to power and the creation of the Roman Empire that stretched from 27 BCE to 476/480 CE in the West and continued in the East until 1453. The Republic officially ended when Caesar was murdered in 44 BCE, and Octavian's reforms ushered in the Pax Romana, a two-century-long period of peace and stability. His reign marked the beginning of the Roman Empire, with key changes including a new calendar, the restructuring of the Senate, and the centralized power effectively controlled by the emperor.