What contribution is General Abner Doubleday known for?

Abner Doubleday (June 26, 1819 -- January 26, 1893) was a career United States Army officer and Union general in the American Civil War. 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. In San Francisco, after the war, he obtained a patent on the cable car railway that still runs there. In his final years in New Jersey, he was a prominent member and later president of the Theosophical Society.

Doubleday is often mistakenly credited with inventing baseball, although he never made such a claim, and there is no evidence to support it.