Complex sentence: Spolin influenced the first generation of improvisational actors at the Second City in Chicago in the late 1950s, through her son, Paul Sills, who was the founding director of the Compass Players which led to the formation of the Second City.
Split into simpler sentences: Spolin influenced the first generation of improvisational actors at the Second City in Chicago in the late 1950s, through her son, Paul Sills. He was the founding director of the Compass Players which led to the formation of the Second City.