Prince William of the House of Schleswig-Holstein-Sonderburg-Glücksburg was elected as Geórgios A´ in 1863, one year after the deposition of the Greek King Otto from the House of Wittelsbach.
He was married to the Grand Duchess Olga Konstantinowna, a granddaughter of the Russian Tsar Nicholas I. This was the first important link between the new dynasty and the Orthodox population.
He also tried to pay attention to the welfare and satisfaction of his new underling, for example by learning the Greek language, getting to know the country and its people on extensive journeys and being very close to the people during his daily walks in Athens.
Despite all this and his efforts to achieve a fairer constitution, Greece remained extremely unstable. During his almost fifty years in power, there were 21 parliamentary elections and 70 different governments.
In foreign policy, he tried to unite all Hellenic populated areas into one state, which naturally led to the hostility of the Ottoman Empire. After initial political successes, he suffered a devastating defeat in the Turkish- Greek War of 1896/97.
Only in the first Balkan War did the Greek army under the crown prince Constantine achieve great military successes and in 1912 George was able to solemnly enter the conquered Thessaloniki. When he walked through the city in the following spring, as always without personal protection, he was shot by the Greek anarchist A. Schinas.
On board the royal yacht Amphitrite, his body was transferred to Athens and buried in the Cathedral of Mariä Annunciation.
His eldest son Constantine I succeeded him.