1521 : Martin Luther excommunicated by pope : On this day in 1521, Pope Leo X issued the papal bull Decet Romanum Pontificem, excommunicating Martin Luther, the German priest whose questioning of certain Roman Catholic practices initiated the Protestant Reformation.
2001 : Hillary Rodham Clinton was sworn in as a U.S. senator from New York, having become the first first lady in U.S. history to win elective office.
1939 : Canadian professional ice hockey player Bobby Hull, the “Golden Jet," was born.
1929 : Italian motion-picture director Sergio Leone, known primarily for his popularization of the “spaghetti western," was born.
1883 : Clement Attlee, British Labour Party leader (1935–55) and prime minister (1945–51), was born.
1777 : The Battle of Princeton (New Jersey) was fought during the American Revolution.
1543 : Spanish soldier and explorer Juan Rodríguez Cabrillo, the ‘‘discoverer" of California, died.