Marcus Aurelius, full name Marcus Aelius Aurelius Antoninus (121-180), Roman emperor (161-180) and Stoic philosopher.

Marcus Aurelius, whose original name was Marcus Annius Verus, was born in Rome on April 20, 121, the nephew by marriage of Antoninus Pius, later emperor. After the latter succeeded to power, he adopted his nephew and married him to his daughter (145). Marcus Aurelius became emperor in 161, and throughout his reign he was engaged in defensive wars on the northern and eastern frontiers of the empire. His legions succeeded in repelling the invasion of Syria by the Parthians in 166, but Rome was again forced into battle in 167 by the Germanic tribes on the Rhine-Danube frontier. Marcus Aurelius returned to Rome intermittently during the German campaign to make legal and administrative reforms. Although he was particularly concerned with public welfare and sold even his personal possessions to alleviate the effects of famine and plague within the empire, he ruthlessly persecuted the Christians, believing them a threat to the imperial system. In 176 he returned to the northern frontier, hoping to extend the boundaries of the empire northeastward to the Wisła (Vistula) river. He died of the plague in Vindobona (now Vienna) on March 17, 180, before he could begin the invasion. His plan was abandoned by his son and successor, Commodus.

In his domestic policy Marcus Aurelius was a champion of the poor, for whom he founded schools, orphanages, and hospitals and alleviated the burden of taxes. He also tried to humanize criminal laws and the treatment of slaves by their masters.

As a philosopher he is remembered for his Meditations, a compendium of 12 books of moral precepts written in Greek. The work, an important formulation of the philosophy of Stoicism, reveals his belief that the moral life leads to tranquillity, and stresses the virtues of wisdom, justice, fortitude, and moderation.