The Principate (27 BC – 284 AD) is the first period of the Roman Empire, extending from the beginning of the reign of Caesar Augustus to the Crisis of the Third Century, after which it was replaced with the Dominate. The Principate is characterized by a concerted effort on the part of the Emperors to preserve the illusion of the formal continuance of the Roman Republic.

It is etymologically derived from the Latin word princeps, meaning chief or first, the political regime dominated by such a political leader, whether or not he is formally head of state and/or head of government. This reflects the Principate Emperors' assertion that they were merely "first among equals" among the citizens of Rome.

In practice, the Principate was a period of enlightened absolutism, with occasional forays into quasi-constitutional monarchy; Emperors tended not to flaunt their power and usually respected the rights of citizens (although they never let this fact bind them).

The title, in full, princeps senatus / princeps civitatis (first amongst the senators, viz., amongst the citizens), was first adopted by Octavian Caesar Augustus (27 BC-AD 14), the first Roman 'Emperor', who chose – like the assassinated dictator Julius Caesar – not to reintroduce a legal monarchy. The purpose was to establish the political stability desperately needed after the exhausting civil wars by a de facto dictatorial regime within the constitutional framework of the Roman Republic as an alternative to the hated early Roman Kingdom.

Julia Agrippina, most commonly referred to as Agrippina Minor or Agrippina the Younger, and after 50 known as Julia Augusta Agrippina (Minor Latin for the ‘younger’, Classical Latin: IVLIA•AGRIPPINA; IVLIA•AVGVSTA•AGRIPPINA, 7 November 15 or 6 November 16 – 19/23 March 59) was a Roman Empress and one of the more prominent women in the Julio-Claudian dynasty. She was a great-granddaughter of the Emperor Augustus, great-niece and adoptive granddaughter of the Emperor Tiberius, sister of the Emperor Caligula, niece and fourth wife of the Emperor Claudius, and mother of the Emperor Nero.

Agrippina the Younger has been described by both the ancient and modern sources as ‘ruthless, ambitious, violent and domineering’. She was a beautiful and reputable woman and according to Pliny the Elder, she had a double canine in her upper right jaw, a sign of good fortune. Many ancient historians accuse Agrippina of poisoning Emperor Claudius, though accounts vary.

Agrippina was the first daughter and fourth living child of Agrippina the Elder and Germanicus. She had three elder brothers, Nero Caesar, Drusus Caesar and the future Emperor Caligula, and two younger sisters, Julia Drusilla and Julia Livilla. Agrippina's two elder brothers and her mother were victims of the intrigues of the Praetorian Prefect Lucius Aelius Sejanus.

Gaius Julius Caesar (Classical Latin: [ˈɡaː.i.ʊs ˈjuː.lɪ.ʊs ˈkaj.sar], July 100 BC – 15 March 44 BC) was a Roman general and statesman and a distinguished writer of Latin prose. He played a critical role in the gradual transformation of the Roman Republic into the Roman Empire.

In 60 BC, Caesar, Crassus and Pompey formed a political alliance that was to dominate Roman politics for several years. Their attempts to amass power through populist tactics were opposed by the conservative elite within the Roman Senate^{[citation needed]}, among them Cato the Younger with the frequent support of Cicero. Caesar's conquest of Gaul, completed by 51 BC, extended Rome's territory to the English Channel and the Rhine. Caesar became the first Roman general to cross both when he built a bridge across the Rhine and conducted the first invasion of Britain.

These achievements granted him unmatched military power and threatened to eclipse Pompey's standing. The balance of power was further upset by the death of Crassus in 53 BC. Political realignments in Rome finally led to a standoff between Caesar and Pompey, the latter having taken up the cause of the Senate. Ordered by the Senate to stand trial in Rome for various charges, Caesar marched on Rome with one legion—legio XIII—from Gaul to Italy, crossing the Rubicon in 49 BC. This sparked a civil war from which he emerged as the unrivaled leader of the Roman world.