The Crimson King pays a role in Hearts, or more accurately his agents. It was published in 99 I think. As I said previously the first book in which the Crimson King is mentioned by name is Insomnia, released in 1994. The first main series Dark Tower book that mentioned him was 1996's Wizard and Glass. However, King did go back and briefly namedrop him in later editions of the first tower book, The Gunslinger. Like IT, Insomnia is also set in Derry, and Mike Hanlon even has a cameo.