Constantine I (272–337), popularly known as Constantine the Great, was a Roman Emperor.
Constantine I may also refer to: Constantine I of Greece (d. 1923) Constantine I Tih (d. 1277), also known as Constantine I of Bulgaria Constantín mac Cináeda (d. 877), also known as Constantine I of Scotland Zara Yaqob (1399–1468), emperor of Ethiopia sometimes known as Constantine I
Nobles on the island of Sardinia Constantine I of Arborea, 11th century ruler in Arborea, on the island of Sardinia Constantine I of Cagliari, 11th century ruler
Nobles in the Kingdom of Georgia Constantine I of Imereti (d. 1327), king of the Imereti in Georgia Constantine I of Georgia (1369–1412), king of Georgia Constantine I of Kakheti (1567–1605), a.k.a. Constantine Khan, King of the Kakheti in Georgia Constantine I, Prince of Mukhrani (fl. 1622 – 1667), a royal of the Bagrationi dynasty of Kartli
People in Cilician Armenia Constantine I, Prince of Armenia (1035–1040), second "Lord of the Mountains" of Cilician Armenia Constantine I of Cilicia (fl. 1221–1267), Catholicos of the Armenian Apostolic Church Constantine I, King of Armenia (1278–1310), also sometimes called Constantine III, King of Cilician Armenia (son of Leo II, and brother of Hethum II)
Religious leaders Patriarch Constantine I of Constantinople (d. 677), patriarch of Constantinople from 675 to 677 Pope Constantine (664–715), Pope from 708 to 715
See also Constantine (disambiguation) Constantius I Constans I