Complex sentence: In 1991, Nickelodeon developed its first animated series, "Doug", "Rugrats" and "The Ren & Stimpy Show"; these series, known as Nicktoons, premiered on August 11,1991.
Split into simpler sentences: In 1991, Nickelodeon developed its first animated series, "Doug", "Rugrats", and "The Ren & Stimpy Show". These series, known as Nicktoons, premiered on August 11,1991.