Marcian was Roman emperor of the East from 450 to 457. Very little of his life before becoming emperor is known, other than that he was a domesticus who served under the commanders Ardabur and his son Aspar for fifteen years. After the death of Emperor Theodosius II on 28 July 450, Marcian was made a candidate for the throne by Aspar, who held much influence because of his military power. After a month of negotiations Pulcheria, Theodosius' sister, agreed to marry Marcian. Zeno, a military leader whose influence was similar to Aspar's, may have been involved in these negotiations, as he was given the high-ranking court title of patrician upon Marcian's accession. Marcian was elected and inaugurated on 25 August 450.

The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title augustus to Octavian in 27 BC. The term "emperor" is a modern convention, and did not exist as such during the Empire. Often when a given Roman is described as becoming emperor in English, it reflects his taking of the title augustus and later basileus. Another title used was imperator, originally a military honorific, and caesar, originally a surname. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.