Hack Wilson was playing for Toledo of the American Association after falling into a slump with the New York Giants. He was left unprotected (some say an oversight), and the Chicago Cubs swooped in and claimed him late in 1925. The Giants loss was the Cubs game as Hack Wilson would win the National League Home Run crown in 1926, a feat he would repeat in 1927, 1928, and 1930. Wilson wasn't just hitting for power as with the exception of 1931, and he never had a season where he batted under .300 or had an OBP under .400. Wilson would twice lead the NL in Walks, and his Slash Line as a Chicago Cub is an incredible .322/.412/.590.
When speaking about Wilson, you have to discuss his 1930 season. That year, he blasted 56 Home Runs, had a 191 RBI (a single-season record), and had a Slash Line of .356/.454/.723. Sadly, Wilson would drink excessively and would become out of shape and was shipped out to the St. Louis Cardinals a year later.
Wilson would enter the Baseball Hall of Fame when he was inducted in 1979 by the Veteran's Committee.