King Constantine may refer to:
Constantine (Briton) (520–523), a king of Dumnonia in sub-Roman Britain Constantine I of Georgia (d. 1412), King of Georgia from 1405 or 1407 until his death Constantine II of Georgia (ca. 1447–1505), of the Bagrationi dynasty, king of Georgia from 1478 Constantine I of Greece (1868–1923), King of Greece from 1913 to 1917 and from 1920 to 1922 Constantine II of Greece (1940–2023), King of Greece from 1964 until abolition of the monarchy of Greece in 1973 Constantine mac Fergusa (d. 820), a king of the Picts Constantine I of Scotland (d. 877), a king of the Picts Constantine II of Scotland (d. 952), an early King of Scotland Constantine III of Scotland (born ca. 970–997), king of Scots from 995 to 997 Constantine I, King of Armenia (r. 1298–1299, d. 1310) Constantine II, King of Armenia (r. 1342–1344), also called Guy Constantine III, King of Armenia (r. 1344–1362) Constantine IV, King of Armenia (r. 1362–1373)