Sam Cooper, a right-handed pitcher from the 1920s, has often been mixed up with another right-hander with the same last name who played for some of the same teams: Darltie Cooper. In fact they were two different players. Here they both are in a detail of the above photo of the Harrisburg Giants (with Darltie identified as “Dottie”):
But while Darltie can be identified pretty readily in a number of official records, Sam was a mystery—until he turned up in the 1930 census. There he is, living in Atlantic City, a professional ballplayer, playing for the “Bacharach ball team.”
He was born ca. 1892 in North Carolina. Unfortunately there are several candidates in the records who could be him, so this is as far as I can get for now; but it’s a start.