Cornelius Alexander Mack (December 22, 1862 - February 8, 1956), born Cornelius Alexander McGillicuddy, was an American baseball player and owner.

Born in East Brookfields, Massachusetts to Irish immigrants, Mack was a journeyman catcher who played 11 seasons in the National League starting in 1886, before he managed the Pittsburgh Pirates from 1894 to 1896 and then, in 1901, took ownership of the Philadelphia Athletics. When New York Giants manager John McGraw called the Athletics "a white elephant nobody wanted," Mack adopted a white elephant as the team's logo, which the Athletics have used off and on ever since.

On the field, Mack was quiet, even-tempered and gentlemanly, serving as a father figure to his players as much as a coach and was universally addressed as "Mr. Mack." Once, when he visited the mound to remove notoriously hot-tempered pitcher Lefty Grove from the game, Grove said, "Go take a [expletive]," when Mack held out his hand for the ball. Mack looked Grove straight in the eye and calmly said, "You go take a [expletive], Robert."

Mack was also tight-fisted. Seeing baseball as a business, he once confided that it was more profitable to have a team get off to a hot start, then ultimately finish fourth. "A team like that will draw well enough during the first part of the season to show a profit for the year, and you don't have to give the players raises when they don't win," he said. The most famous example of Mack's tight-fistedness came on July 10, 1932, when the Athletics played a one-game series with the Cleveland Indians. To save train fare, Mack only brought two pitchers. The starting pitcher was knocked out of the game in the first inning, leaving only knuckleballing relief pitcher Eddie Rommel. Rommel pitched 17 innings and gave up 33 hits, but won the game, 18-17.

Mack managed the Athletics until 1951, when he retired at age 81. He won the World Series five times, building two dynasties that lasted from 1910-1914 (which featured Mack's famous "$100,000 infield" of Eddie Collins, Home Run Baker, Jack Barry and Stuffy McInnis) and again in 1929-1931 (which featured Hall of Famers Grove, Mickey Cochrane, Jimmie Foxx and Al Simmons). His 1911 and 1929 teams are considered by many to be among the greatest baseball teams of all time, and his 3,776 lifetime wins are a major league record—as are his 4,025 losses and 7878 games managed.

Mack twice dismantled his dynasties; the first out of outrage when some of his star players started signing lucrative contracts with upstart Federal League teams, and the second due to financial difficulties due to the Great Depression. Besides his five World Series wins and four pennants, Mack's teams also finished last 17 times.

Mack was elected to the Baseball Hall of Fame in 1937.

Mack's grandson, Connie Mack III (born October 29, 1940 in Philadelphia, Pennsylvania) was a Republican member of the United States House of Representatives from 1983 to 1989 and of the United States Senate from 1989 to 2001, all from Florida.