George I (Greek: Γεώργιος Α΄, Βασιλεύς των Ελλήνων, Geórgios Α΄, Vasiléfs ton Ellínon; 24 December 1845 – 18 March 1913) was King of Greece from 1863 to 1913. Originally a Danish prince, George was only 17 years old when he was elected king by the Greek National Assembly, which had deposed the former king Otto. His nomination was both suggested and supported by the Great Powers (the United Kingdom of Great Britain and Ireland, the Second French Empire and the Russian Empire). He became the first monarch of a new Greek dynasty.

George's reign of almost 50 years (the longest in modern Greek history) was characterized by territorial gains as Greece established its place in pre-World War I Europe. During the First Balkan War, he was assassinated. In sharp contrast to his own reign, the reigns of his successors proved short and insecure.

George was born in Copenhagen, and was the second son of Prince Christian of Schleswig-Holstein-Sonderburg-Glücksburg and Louise of Hesse-Kassel (or Hesse-Cassel). Although his full name was Prince Christian Wilhelm Ferdinand Adolf Georg of Schleswig-Holstein-Sonderburg-Glücksburg (Greek: Χριστιανός Γουλιέλμος Φερδινάνδος Αδόλφος Γεώργιος), until his accession in Greece, he was known as Prince Vilhelm (William), the namesake of his paternal and maternal grandfathers,Frederick William, Duke of Schleswig-Holstein-Sonderburg-Glücksburg, and Prince William of Hesse.

Greece ⁱ/ˈɡriːs/ (Greek: Ελλάδα, Ellada, IPA: [eˈlaða] ( listen) historically in Katharevousa and Ancient Greek: Ἑλλάς, Hellas, IPA: [eˈlas] and [helːás] respectively), officially the Hellenic Republic (Ελληνική Δημοκρατία, Elliniki Dimokratia, IPA: [eliniˈci ðimokraˈtia]), is a country in Southern Europe, politically considered part of Western Europe.Athens is the capital and the largest city in the country (its urban area also including Piraeus). The population of the country is around 11 million.

Greece has land borders with Albania, the Republic of Macedonia and Bulgaria to the north, and Turkey to the east. The Aegean Sea lies to the east of mainland Greece, the Ionian Sea to the west, and the Mediterranean Sea to the south. Greece has the 11th longest coastline in the world at 13,676 km (8,498 mi) in length, featuring a vast number of islands (approximately 1,400, of which 227 are inhabited), including Crete, the Dodecanese, the Cyclades, and the Ionian Islands among others. Eighty percent of Greece consists of mountains, of which Mount Olympus is the highest at 2,917 m (9,570 ft).

George III (George William Frederick; 4 June 1738 – 29 January 1820) was King of Great Britain and King of Ireland from 25 October 1760 until the union of these two countries on 1 January 1801, after which he was King of the United Kingdom of Great Britain and Ireland until his death. He was concurrently Duke and prince-elector of Brunswick-Lüneburg ("Hanover") in the Holy Roman Empire until his promotion to King of Hanover on 12 October 1814. He was the third British monarch of the House of Hanover, but unlike his two Hanoverian predecessors he was born in Britain, spoke English as his first language, and never visited Hanover.

His life and reign, which were longer than those of any previous British monarch, were marked by a series of military conflicts involving his kingdoms, much of the rest of Europe, and places farther afield in Africa, the Americas and Asia. Early in his reign, Great Britain defeated France in the Seven Years' War, becoming the dominant European power in North America and India. However, many of its American colonies were soon lost in the American War of Independence. Further wars against revolutionary and Napoleonic France from 1793 concluded in the defeat of Napoleon at the Battle of Waterloo in 1815.

Grand Duchess Olga Constantinovna of Russia (Russian: Великая Княжна Ольга Константиновна), later Queen Olga of the Hellenes (Greek: Βασίλισσα Όλγα των Ελλήνων) (3 September [O.S. 22 August] 1851 – 18 June 1926), was the queen consort of King George I of Greece and briefly in 1920, Queen Regent of Greece. She is the great-grandmother of Queen Sofia of Spain, the paternal grandmother of Prince Philip, Duke of Edinburgh, and the great-grandmother of Charles, Prince of Wales, heir apparent to the British throne.

She was born in Pavlovsk to Grand Duke Konstantin Nikolayevich of Russia and Grand Duchess Alexandra Iosifovna, a former princess of Saxe-Altenburg. She was a granddaughter of Tsar Nicholas I and first cousin of Tsar Alexander III. The young King George I of Greece visited Russia in 1863 to thank her uncle Tsar Alexander II for his support during George's election to the throne of Greece. Whilst there, George met the then twelve-year old Olga for the first time.

George visited Russia again in 1867 to meet with his sister Dagmar, who had married Tsarevitch Alexander the year before. George and Olga fell in love and married on 27 October 1867 (Gregorian calendar), when she was sixteen years old.

George II (Greek: Γεώργιος Βʹ, Βασιλεὺς τῶν Ἑλλήνων, Geórgios Βʹ, Vasiléfs ton Ellínon; 20 July 1890 – 1 April 1947) reigned as King of Greece from 1922 to 1924 and from 1935 to 1947.

George was born at the royal villa at Tatoi, near Athens, the eldest son of King Constantine I of Greece and his wife, Princess Sophia of Prussia. George pursued a military career, training with the Prussian Guard at the age of 18, then serving in the Balkan War as a member of the 1st Greek Infantry. When his grandfather was assassinated in 1913, George became the crown prince (Diadochos) as well as the Duke of Sparta.

After a coup deposed King Constantine during the First World War, Crown Prince George, by then a Major, followed his father into exile in 1917 (see National Schism); his brother Alexander was installed as king by prime minister Eleftherios Venizelos, an avowed Republican.

When Alexander I died following an infection from a monkey bite in 1920, Venezelos was voted out of office, and a plebiscite restored Constantine to the throne. Crown Prince George served as a colonel, and later a major general in the war against Turkey. During this time he married his second cousin, on 27 February 1921 in Bucharest, Princess Elisabeth of Romania, daughter of King Ferdinand and Queen Marie of Romania. When the Turks defeated Greece at the Battle of Dumlupınar, the military forced the abdication of Constantine, and George succeeded to the Greek throne on 27 September 1922.