 Sullivan is considered a pioneer of early baseball; he founded both the Northwest League and the Texas League, both minor leagues that still exist and thrive today.Credited with discovering Charles Comiskey, he is considered by some to be the first person to emphasize the importance of scouting.Comiskey joined the St. Louis Browns in , and replaced Sullivan as the team's manager in mid-; it had been Sullivan's first managerial post, as he compiled a record of 53-26 to begin the year.