George III of the United Kingdom

George III was born in 1738, the first Hanover monarch raised in Britain who spoke English as his first language. He became king in 1760 at twenty-two and married Princess Charlotte of Mecklenburg-Strelitz the next year; they had 15 children. His early reign brought triumph in the Seven Years' War, making Britain the dominant power in North America and India. Then came the disaster that defined him: the loss of thirteen American colonies in the War of Independence. He fought on through the Napoleonic Wars until Waterloo in 1815 and oversaw the 1807 ban on the transatlantic slave trade and the 1800 union of Great Britain and Ireland. In his later years, recurrent mental illness - possibly bipolar disorder or porphyria - took hold. By 1810 he suffered a final relapse and never recovered; his eldest son became Prince Regent in 1811. George died in 1820 at eighty-one, still the longest-lived and longest-reigning male monarch Britain has known.