Complex sentence: After his playing career, Mikan became one of the founders of the American Basketball Association (ABA), serving as commissioner of the league, and was also vital for the forming of the Minnesota Timberwolves.
Split into simpler sentences: After his playing career, Mikan became one of the founders of the American Basketball Association (ABA), serving as commissioner of the league. He was also vital for the forming of the Minnesota Timberwolves.