Three main players in the political history of the Roman Empire were Julius Caesar, Augustus, and Marcus Aurelius.

1. Julius Caesar:
Julius Caesar was a Roman general and statesman who played a crucial role in the demise of the Roman Republic and the rise of the Roman Empire. He is known for his military conquests, political reforms, and his assassination. Caesar's military campaigns expanded the Roman Empire to its greatest territorial extent, including the conquest of Gaul (modern-day France), and his victories in the civil war against Pompey the Great led to his appointment as dictator for life. He implemented various reforms, such as the Julian calendar, to improve the functioning of the state. However, his concentration of power and his disregard for the traditional Republican institutions led to his assassination in 44 BCE.

2. Augustus:
Augustus, originally known as Octavian, was the first Roman emperor and the founder of the Roman Empire. He was the adopted son of Julius Caesar and emerged as the sole ruler after defeating his rivals in the civil war. Augustus reformed and centralized the government, establishing the principate system, which laid the foundation for the imperial system that lasted for centuries. He implemented various administrative, economic, and military reforms that stabilized the empire and brought about a period of relative peace and prosperity known as the Pax Romana. Augustus also initiated significant building projects, such as the reconstruction of Rome and the construction of grand monuments like the Pantheon. His rule set the precedent for future emperors and his reign is often considered the beginning of the Roman Empire.

3. Marcus Aurelius:
Marcus Aurelius was a Roman emperor who ruled from 161 to 180 CE. He is known for his philosophical writings and his reign during a time of significant challenges to the Roman Empire. Marcus Aurelius faced invasions from Germanic tribes and conflicts along the eastern frontier. Despite these challenges, he is often remembered as a philosopher-king and a Stoic philosopher. His collection of writings, known as "Meditations," reflect his thoughts on ethics, self-discipline, and the pursuit of virtue. Marcus Aurelius' reign marked the end of the Pax Romana and the beginning of a period of decline for the Roman Empire. However, his philosophical teachings have had a lasting influence and continue to be studied today.

These three figures played crucial roles in shaping the political history of the Roman Empire, with Julius Caesar laying the groundwork for the transition from the Republic to the Empire, Augustus establishing the imperial system, and Marcus Aurelius ruling during a challenging period while leaving behind a philosophical legacy.