Domitian (/dəˈmɪʃən, -iən/ də-MISH-ən, -⁠ee-ən; Latin: Domitianus; 24 October 51 – 18 September 96) was Roman emperor from 81 to 96. The son of Vespasian and the younger brother of Titus, his two predecessors on the throne, he was the last member of the Flavian dynasty. Described as "a ruthless but efficient autocrat", his authoritarian style of ruling put him at sharp odds with the Senate, whose powers he drastically curtailed.

Domitian had a minor and largely ceremonial role during the reigns of his father and brother. After the death of his brother, Domitian was declared emperor by the Praetorian Guard. His 15-year reign was the longest since Tiberius. As emperor, Domitian strengthened the economy by revaluing the Roman coinage, expanded the border defenses of the empire, and initiated a massive building program to restore the damaged city of Rome. Significant wars were fought in Britain, where his general Agricola made significant gains in his attempt to conquer Caledonia (Scotland), and in Dacia (Modern-day Romania), where Domitian was unable to achieve a decisive victory against King Decebalus. Domitian's government exhibited strong authoritarian characteristics. Religious, military, and cultural propaganda fostered a cult of personality, and by nominating himself as perpetual censor, he sought to control public and private morals.

As a consequence, Domitian was popular with the people and the army, but considered a tyrant by members of the Roman Senate. Domitian's reign came to an end in 96 when he was assassinated by court officials. He was succeeded the same day by his advisor Nerva. After his death, Domitian's memory was condemned to oblivion by the Senate, while senatorial and equestrian authors such as Tacitus, Pliny the Younger, and Suetonius propagated the view of Domitian as a cruel and paranoid tyrant. Modern revisionists have instead characterized Domitian as a ruthless but efficient autocrat whose cultural, economic, and political programs provided the foundation of the peaceful second century.

Domitian was born in Rome on 24 October 51, the youngest son of Titus Flavius Vespasianus—commonly known as Vespasian—and Flavia Domitilla Major. He had an older sister, Domitilla the Younger, and brother, also named Titus Flavius Vespasianus. Decades of civil war during the 1st century BC had contributed greatly to the demise of the old aristocracy of Rome, which a new Italian nobility gradually replaced in prominence during the early part of the 1st century. One such family, the Flavians, or Flavia gens, rose from relative obscurity to prominence in just four generations, acquiring wealth and status under the emperors of the Julio-Claudian dynasty.

Domitian's great-grandfather, Titus Flavius Petro, had served as a centurion under Pompey during Caesar's civil war. His military career ended in disgrace when he fled the battlefield at the Battle of Pharsalus in 48 BC. Nevertheless, Petro managed to improve his status by marrying the extremely wealthy Tertulla, whose fortune guaranteed the upward mobility of Petro's son Titus Flavius Sabinus, Domitian's grandfather. Sabinus himself amassed further wealth and possible equestrian status through his services as tax collector in Asia and banker in Helvetia (modern Switzerland). By marrying Vespasia Polla he allied the Flavian family to the more prestigious gens Vespasia, ensuring the elevation of his sons Titus Flavius Sabinus and Vespasian to senatorial rank.

The political career of Vespasian included the offices of quaestor, aedile, and praetor, and culminated in a consulship in 51, the year of Domitian's birth. As a military commander, Vespasian gained early renown by participating in the Roman invasion of Britain in 43. Nevertheless, ancient sources allege poverty for the Flavian family at the time of Domitian's upbringing, even claiming Vespasian had fallen into disrepute under the emperors Caligula (37–41) and Nero (54–68). Modern history has refuted these claims, suggesting these stories later circulated under Flavian rule as part of a propaganda campaign to diminish success under the less reputable Emperors of the Julio-Claudian dynasty and to maximize achievements under Emperor Claudius (41–54) and his son Britannicus.

By all appearances, the Flavians enjoyed high imperial favour throughout the 40s and 60s. While Titus received a court education in the company of Britannicus, Vespasian pursued a successful political and military career. Following a prolonged period of retirement during the 50s, he returned to public office under Nero, serving as proconsul of the Africa Province in 63, and accompanying the emperor Nero during an official tour of Greece in 66. That same year Jews from the Province of Judaea revolted against the Roman Empire, sparking what is now known as the First Jewish–Roman War. Vespasian was assigned to lead the Roman army against the insurgents, with Titus—who had completed his military education by this time—in charge of a legion.

Of the three Flavian emperors, Domitian would rule the longest, despite the fact that his youth and early career were largely spent in the shadow of his older brother. Titus had gained military renown during the First Jewish–Roman War. After their father Vespasian became emperor in 69 following the civil war known as the Year of the Four Emperors, Titus held a great many offices, while Domitian received honours, but no responsibilities. By the time he was 16 years old, Domitian's mother and sister had long since died, while his father and brother were continuously active in the Roman military, commanding armies in Germania and Judaea. For Domitian, this meant that a significant part of his adolescence was spent in the absence of his near relatives.