HBO has several "Game of Thrones" spin-offs in development. The series' first spin-off, a prequel called "House of the Dragon," premieres August 21 on HBO and HBO Max.  Other "Game of Thrones" spin-offs in development include an untitled Jon Snow sequel series starring Kit Harington, as well as "The Sea Snake," "Ten Thousand Ships," "The Hedge Knight," and "The Golden Empire." None of these shows have been officially ordered to series just yet, but all of them come from stories and characters created by George R.R. Martin.