Charles the Fat

Charles was the youngest son of Louis the German and a great-grandson of Charlemagne, granted Alamannia in 876 when East Francia was carved up. He took Italy after his brother Carloman had a stroke and abdicated, then got crowned emperor by Pope John VIII in 881. When his brother Louis the Younger died the next year, Charles reunited East Francia; when his cousin Carloman II died in 884, he inherited West Francia too - the whole Carolingian map back under one man. Frequently ill and likely epileptic, he twice bought peace with Viking raiders instead of fighting, most notoriously at the Siege of Paris. In November 887 his nephew Arnulf of Carinthia led a coup and stripped him of East Francia, Lotharingia, and Italy. Charles retired quietly and died of natural causes eight weeks later, on 13 January 888. The empire fractured into five successor kingdoms immediately and would not be reunited until Napoleon.