Alexander Cartwright was an American baseball player and a key figure in the development of modern baseball. Born on April 17, 1820, in New York City, he is best known for formalizing the rules of the game and establishing the first organized baseball team, the Knickerbocker Base Ball Club, in 1845. Cartwright's contributions included the introduction of the diamond-shaped infield and the three-strike rule. His efforts helped transform baseball from a casual pastime into a structured sport, laying the groundwork for the National League and the professional game we know today.