Union Gen. Abner Doubleday (June 26, 1819 – January 26, 1893). He fired the first shot in defense of Fort Sumter, the opening battle of the war, and had a pivotal role in the early fighting at the Battle of Gettysburg. Gettysburg was his finest hour, but his relief by Maj. Gen. George G. Meade caused lasting enmity between the two men.
Abner Doubleday is probably best known as the inventor of baseball, though he was not. In 1907, a panel of baseball experts headed by A. G. Spalding conducted a highly-publicized investigation into the origins of the game, and concluded that Doubleday had written the rules for baseball in 1839 in Cooperstown, New York (where the Baseball Hall of Fame was later constructed).