Ferdinand I of Portugal

Ferdinand became King of Portugal in 1367 at twenty-one, already known as "the Handsome." Four years later he briefly claimed the crown of Galicia, holding onto that title until 1373 even after the claim went cold. The other nickname, "the Inconstant," stuck for reasons the record hints at but doesn't spell out. What mattered in the end was simpler: no legitimate sons. When he died in October 1383, two weeks shy of his thirty-eighth birthday, the throne had no clear successor, and Portugal tipped straight into the crisis that would define the next two years.