Complex sentence: The Crimson King, also commonly known as Los is a fictional character created by Stephen King, he is the antagonist in the novel Insomnia and one of the main villains in the latter half of Stephen King's "Dark Tower" series.
Split into simpler sentences: The Crimson King, also commonly known as Los, is a fictional character created by Stephen King. He is the antagonist in the novel Insomnia and one of the main villains in the latter half of Stephen King's "Dark Tower" series.