This is a marble ancient bust of Marcus Aurelius, called the Philosopher, Roman emperor from 161 to 180. He was adopted by Antoninus Pius, whose daughter Faustina he married and whom he and his adoptive brother, Lucius Verus, succeeded. He ruled with Lucius until Lucius' death in 169, and with his son by Faustina, Commodus, from 177. He was the last of the rulers traditionally known as the Five Good Emperors.
He was a practitioner of Stoicism. His personal philosophical writings, which later came to be called Meditations, are a significant source of the modern understanding of ancient Stoic philosophy. They have been seen as one of the greatest works of philosophy.
During his reign, the Roman Empire defeated a revitalized Parthian Empire in the East; Marcus' general Avidius Cassius sacked the Parthian capital Ctesiphon in 164. In central Europe, Marcus fought the Marcomanni, Quadi, and Sarmatians with success during the Marcomannic Wars, although the threat of the Germanic peoples began to represent a troubling reality for the Empire. Persecution of Christians is said to have increased during his reign.
His death in 180 is seen as an end to the Pax Romana. The increasing instability in the West that followed has traditionally been seen as the beginning of the eventual fall of the Western Roman Empire.