As king and queen, George and Mary saw Britain through World War I, a difficult time for the royal family as they had many German relatives. Queen Mary was born in Germany, as had been George's grandfather, Prince Albert of Saxe-Coburg-Gotha. In 1917, the decision was made to change the name of the Royal House from the German-sounding Saxe-Coburg-Gotha, courtesy of Queen Victoria's marriage, to Windsor. (The Royal Family's personal surname was also changed, from Wettin to Windsor; in 1960 the personal surname of the descendants of Queen Elizabeth II was further changed to Mountbatten-Windsor.)
Following the war, George's health began to deteriorate. He had always had a weak chest, and this weakness was exacerbated by his heavy smoking. But he managed to see the silver jubilee of his reign, in 1935, by which time he had become a well-loved king. He died on January 20, 1936, at Sandringham House and is buried at Windsor Castle. He was succeeded by his eldest son, Edward VIII.
King George also reigned as King in many states, including the Irish Free State, becoming 'King of Ireland' under the Royal Titles Act. An astute judge of people, he once advised Ireland's High Commissioner in London to send a personal message from him to Eamon de Valera: "Don't make so many promises. They are so damned difficult to carry out." "Too true", de Valera is supposed to have remarked with a laugh. "I could do with someone like His Majesty in my cabinet!"
George was a well-known stamp collector, and played a large role in building the Royal Philatelic Collection into the most comprehensive assemblage of United Kingdom and Commonwealth stamps in the world, in some cases setting record purchase prices for items. His enthusiasm for stamps, though denigrated by the intelligentsia, did much to popularize the hobby.