Jesse "Pop" Haines was a pitcher in the National League from 1918 to 1937. Aside from a one game cup of coffee with the Reds he spent his entire career with the St. Louis Cardinals, during which he helped them to five pennants and three World Series victories. He won 210 games, second behind Bob Gibson on the club list.
Haines, who didn't become a major league regular until he was 26, got by with a solid fastball and a knuckleball he actually gripped with his knuckles. (Most knuckleballers of today grip it with their fingernails, the exception being Jared Fernandez, whose knuckler is similar to Haines'.) This unorthodox grip allowed him to throw a "hard" knuckleball. He pitched to varying degrees of success until he was 43; this earned him his nickname.
Pop was elected to the Hall of Fame in 1970, and his numbers make him quite the stretch. However, the Veterans Committee made a lot of stretches with Frankie Frisch at the helm--the Fordham Flash spearheaded the campaigns for a lot of his former teammates, Haines included, even though they had ridiculously poor numbers for the Hall of Fame. Jesse Haines may not have been great, but he was certainly very good, and an important part of the Gashouse Gang Cardinals teams of the 1930s.
Major League Baseball Hall of Fame
Chick Hafey | Billy Hamilton
Sources: www.baseball-reference.com, www.baseballlibrary.com, Bill James' Whatever Happened to the Hall of Fame, prev. The Politics of Glory.