Tim Keefe, RHP
Career: 1880-93, Giants, Phillies, others
Fun fact: Record-holder for winning a game in the most ballparks (47)
If you include everyone who played before the distance between the mound and plate was 60 feet 6 inches, you have to make room for Keefe, a 19th century gent dominant from 45 and 50 feet.
Keefe won three ERA titles and had a run of 32 or more wins in six straight seasons, topping out at 42 in 1886.