Lewis Robert "Hack" Wilson (April 26, 1900 – November 23, 1948) was an American Major League Baseball player who played 12 seasons for the New York Giants, Chicago Cubs, Brooklyn Dodgers and Philadelphia Phillies. Despite his diminutive stature, he was one of the most accomplished power hitters in the game during the late 1920s and early 1930s. His 1930 season with the Cubs is widely considered one of the most memorable individual single-season hitting performances in baseball history. Highlights included 56 home runs, the National League record for 68 years, and 191 runs batted in, an MLB record yet to be approached; the closest any player has come to having that many RBIs came in the very next season, when Lou Gehrig had 185 for the New York Yankees. "For a brief span of a few years," wrote a sportswriter of the day, "this hammered down little strongman actually rivaled the mighty Ruth."

While Wilson's combativeness and excessive alcohol consumption made him one of the most colorful sports personalities of his era, his drinking and fighting undoubtedly contributed to a premature end to his athletic career and, ultimately, his premature death. He was inducted into the Baseball Hall of Fame in 1979.

Lewis Robert Wilson was born April 26, 1900, in the Pennsylvania steel mill town of Ellwood City, north of Pittsburgh. His mother, Jennie Kaughn, 16, was an unemployed drifter from Philadelphia; his father, Robert Wilson, 24, was a steel worker. His parents never married; both were heavy drinkers, and in 1907 his mother died of appendicitis at the age of 24.

In 1916, Wilson left school to take a job at a locomotive factory, swinging a sledge hammer for four dollars a week. Although only 5 ft 6 in (1.68 m) tall, he weighed 195 lb (88 kg) with an 18-inch neck, and feet that fit into size 5+1⁄2 shoes. Sportswriter Shirley Povich later observed that he was "built along the lines of a beer keg, and was not wholly unfamiliar with its contents." While his unusual physique was considered an oddity at the time, his large head, tiny feet, short legs, and broad, flat face are now recognized as hallmarks of fetal alcohol syndrome.

In 1921, Wilson moved to Martinsburg, West Virginia, to join the Martinsburg Mountaineers of the Class "D" Blue Ridge League. After breaking his leg while sliding into home plate during his first professional game, he was moved from the catcher's position to the outfield. In 1922, he met Virginia Riddleburger, a 34-year-old office clerk; they married the following year. In 1923, playing for the "B" division Portsmouth Truckers, he led the Virginia League in hitting with a .388 batting average. Late in the season, New York Giants manager John McGraw purchased his contract from Portsmouth for $10,500 (equivalent to $590,000 in 2025).

Wilson made his major league debut with the Giants on September 29, 1923, at the age of 23, and became the starting left fielder the following season. By mid-July he was ranked second in the National League (NL) in hitting. He ended the season with a .295 average, 10 home runs, and 57 runs batted in (RBIs) as New York won the NL pennant. In the 1924 World Series he averaged only .233 in a seven-game loss to the Washington Senators.

Multiple stories exist to explain the origin of Wilson's nickname. By one account, a New York newspaper held a nicknaming contest; the winning entry was "Hack" because he reminded many fans of another stocky athlete, the popular wrestler Georg Hackenschmidt. In another version, McGraw is said to have remarked that Wilson's physique was reminiscent of a "hack" (slang for taxicab in that era). Giants teammate Bill Cunningham claimed that the nickname was based on Wilson's resemblance to Hack Miller, an outfielder with the Chicago Cubs. The New York Times printed the first documented usage of "Hack" on June 10, 1924.

Early in the 1925 season, Wilson hit the longest home run on record at Ebbets Field against the Brooklyn Robins, but fell into a slump in May, and was replaced in left field by Irish Meusel. On July 2, Wilson hit two home runs in one inning, tying Ken Williams' major league record set in 1922, but his hitting slump continued. In August, McGraw told reporters that he had "... made the mistake of rushing [Wilson] along," and sent him to the Giants' minor league affiliate, the Toledo Mud Hens of the American Association. At season's end, a front office oversight — or possibly, deliberate inaction — left him unprotected on the Toledo roster, and the last-place Chicago Cubs acquired him on waivers. "They let go the best outfielder I ever played alongside," said Giants right fielder Ross Youngs, "and they're going to regret it."