Of course there have been many Cubs players over the years who went by the nickname "Lefty," but here are two of the most prominent...

Lefty Minner (1951-1957) The big 6'4" pitcher's real name was Paul, and he pitched for the Cubs for seven seasons. Just like every ballplayer named lefty, Minner was a left-handed pitcher. He was big and strong, and had a couple of very respectable years for the Cubs, including 1952 when he was 14-9. It's true he was 17 games under .500 in his other six years, but those were some unbelievably lousy teams. His ERA was always respectable.

Lefty Tyler (1918-1921) His real name was George, but everyone called him Lefty. He was in his 8th major league season when he came to the Cubs (from the Boston Braves). He had one great season for the Cubs, going 19-8 in 1918, and pitched well in the World Series that year, but developed a strange shoulder injury the next year. He was sent to Minnesota by the Cubs to get examined at the Mayo Clinic. They said there was nothing wrong with his shoulder...his problems were caused by unusually bad teeth. They extracted almost all of his teeth to cure his shoulder injury, which amazingly, didn't do the trick. He was never the same after that.