Hadrian ( 24 January 76 – 10 July 138) was Roman emperor from 117 to 138. Hadrian was born in Italica, close to modern Seville in Spain, an Italic settlement in Hispania Baetica; his branch of the Aelia gens, the Aeli Hadriani, came from the town of Hadria in eastern Italy. He was a member of the Nerva-Antonine dynasty.

Early in his political career, and several years before Trajan became emperor, Hadrian married Vibia Sabina, Trajan's grandniece. The marriage and Hadrian's later succession as emperor were probably promoted by Trajan's wife Pompeia Plotina. Soon after his own succession, Hadrian had four leading senators unlawfully put to death, probably because they seemed to threaten the security of his reign; this earned him the senate's lifelong enmity. He earned further disapproval by abandoning Trajan's expansionist policies and territorial gains in Mesopotamia, Assyria, Armenia, and parts of Dacia. Hadrian preferred to invest in the development of stable, defensible borders and the unification of the empire's disparate peoples as subjects of a panhellenic empire, led by Rome.

Hadrian energetically pursued his own Imperial ideals and personal interests. He visited almost every province of the Empire, and indulged a preference for direct intervention in imperial and provincial affairs, especially building projects. He is particularly known for building Hadrian's Wall, which marked the northern limit of Britannia. In Rome itself, he rebuilt the Pantheon and constructed the vast Temple of Venus and Roma. In Egypt, he may have rebuilt the Serapeum of Alexandria. As an ardent admirer of Greek culture, he promoted Athens as the cultural capital of the Empire. His intense relationship with Greek youth Antinous and the latter's untimely death led Hadrian to establish a widespread, popular cult. Late in Hadrian's reign, he suppressed the Bar Kokhba revolt; he saw this rebellion as a failure of his panhellenic ideal.

Hadrian's last years were marred by chronic illness. His marriage had been both unhappy and childless. In 138 he adopted Antoninus Pius and nominated him as a successor, on condition that Antoninus adopt Marcus Aurelius and Lucius Verus as his own heirs. Hadrian died the same year at Baiae, and Antoninus had him deified, despite opposition from the Senate. Later historians counted him as one of Rome's so-called "Five Good Emperors", and as a "benevolent dictator". His own Senate found him remote and authoritarian. He has been described as enigmatic and contradictory, with a capacity for both great personal generosity and extreme cruelty and driven by insatiable curiosity, conceit, and ambition.