King of Greece from 1964 until the abolition of the monarchy in 1973. He is also from birth a Prince of Denmark.
He succeeded his father Paul in March 1964. Although the accession of the young monarch was initially regarded auspiciously, his reign soon became controversial: Constantine's involvement in the Apostasia of July 1965 created unrest among sections of the population and aggravated the ongoing political instability that culminated in the Colonels' Coup of 21 April 1967.
The coup was successful leaving Constantine, as head of state, little room to manoeuvre as he had no loyal military forces to rely on. As a result he reluctantly agreed to inaugurate the putschist government on the condition that it be made up largely of civilian ministers. On 13 December 1967, he was forced to flee the country following an abortive counter-coup against the junta. He remained in exile the head of state until 1 June 1973, when the junta abolished the monarchy.
Link to Wikipedia biography
