Arley Wilbur Cooper (February 24, 1892 – August 7, 1973) was an American starting pitcher in Major League Baseball who played most of his career for the Pittsburgh Pirates.

He established NL records for left-handers – second only to Eddie Plank among all southpaws – for career wins (216), innings pitched (3466+1⁄3) and games started (405); all were broken within several years by Eppa Rixey.

He began his professional career in 1911 with the Marion, Ohio based Marion Diggers minor league team partially owned by future U.S. President Warren G. Harding; some reports suggested that Harding was the person who recommended Cooper to the Pirates, although he pitched for another minor league team before reaching the majors.

Also known as an excellent fielder, in 1920 he became the only pitcher in major league history to begin two triple plays in a single season (on July 7 and August 21), and in 1924 he picked off a record seven runners at third base; that year the Pirates finished within three games of first place, the closest he would come to a championship.

In October 1924, Cooper was traded to the Chicago Cubs, along with Charlie Grimm and Rabbit Maranville, in a decidedly unpopular six-player deal; he was greatly disappointed to leave the Pirates, and never pitched as effectively again.