Complex sentence: During this period, J. Stuart Blackton not only ran the Vitagraph studio, but also produced, directed, wrote, and even starred in his films, playing the comic strip character "Happy Hooligan" in a series of shorts.
Split into simpler sentences: During this period, J. Stuart Blackton was not only running the Vitagraph studio, but also producing, directing, writing, and even starring in his films. He played the comic strip character "Happy Hooligan" in a series of shorts.