Alexander Joy Cartwright Jr. (April 17, 1820 – July 12, 1892) was a founding member of the New York Knickerbockers Base Ball Club in the 1840s. Although he was an inductee of the Baseball Hall of Fame and he was sometimes referred to as a "father of baseball", the importance of his role in the development of the game may have been exaggerated.
The rules of the modern game were long considered to have been based on the Knickerbocker Rules developed in 1845 by Cartwright and a committee from the Knickerbockers. However, later research called this scenario into question. The myth of Abner Doubleday having invented baseball was believed by many, but in Cooperstown in 1939, the myth was debunked. Cartwright (unlike Doubleday) was inducted into the Hall of Fame as a pioneering contributor to the game, 46 years after his death. Although it has been stated that Cartwright was officially declared the inventor of the modern game of baseball by the 83rd United States Congress on June 3, 1953, the Congressional Record, the House Journal, and the Senate Journal from June 3, 1953, did not mention Cartwright.