|King of the Hellenes|
|First reign||18 March 1913 – 11 June 1917|
|Second reign||19 December 1920 – 27 September 1922|
|Born||2 August 1868|
Athens, Kingdom of Greece
|Died||11 January 1923 (aged 54)|
Palermo, Kingdom of Italy
|Burial||14 January 1923|
Sophia of Prussia (m. 1889)
|Father||George I of Greece|
|Mother||Olga Constantinovna of Russia|
Constantine I (Greek: Κωνσταντίνος Αʹ, Konstantínos I; 2 August [O.S. 21 July] 1868 – 11 January 1923) was King of Greece from 18 March 1913 to 11 June 1917 and from 19 December 1920 to 27 September 1922.
He was commander-in-chief of the Hellenic Army during the unsuccessful Greco-Turkish War of 1897 and led the Greek forces during the successful Balkan Wars of 1912–1913. He then led the Greek forces in Anatolia during the Greco-Turkish War of 1919-1922. His forces conquered much of western Asia Minor and almost reached Ankara but failed to take the city.