Constantine V (718 – September 14, 775) was Byzantine Emperor from 741 to 775; Greek: Κωνσταντίνος Ε΄, Kōnstantinos V); (he was denigrated by his enemies as Kopronymos or Copronymus meaning the dung-named).

Constantine was born in Constantinople, the son and successor of Emperor Leo III and Maria. In August 720 he was associated on the throne by his father, who had him marry Tzitzak, daughter of the Khazar khagan Bihar. His new bride was baptized as Irene (Eirēnē, "peace") in 732. Constantine V succeeded his father as sole emperor on April 19, 741.

Constantine was crossing Asia Minor to campaign against the Umayyad Caliphate under Hisham ibn Abd al-Malik on the eastern frontier in June 741 or 742. But during this course Constantine was attacked by the forces of his brother-in-law Artabasdos, the stratēgos of the Armeniac theme. Artabasdos was the husband of Anna, an older sister of Constantine.

Defeated, Constantine sought refuge in Amorion, while the victor advanced on Constantinople and was accepted as Emperor. While Constantine now received the support of the Anatolic and Thracesian themes, Artabasdos secured that of the themes of Thrace and Opsikion, in addition to his own Armeniac soldiers.