So, how’d those White Walkers get their start? HBO viewers may soon find out.

The premium cable channel announced on Friday that it would make a pilot for one of the five “Game of Thrones” prequels it has in development.

The pilot will take place “thousands of years before the events of ‘Game of Thrones,’” the network said in a statement. It did not say when the pilot might air.

“The series chronicles the world’s descent from the golden Age of Heroes into its darkest hour,” HBO added. “And only one thing is for sure: From the horrifying secrets of Westeros’s history to the true origin of the White Walkers, the mysteries of the East to the Starks of legend … it’s not the story we think we know.”

George R. R. Martin, the author of the “Game of Thrones” books, wrote the story for the pilot, along with Jane Goldman. Ms. Goldman, the co-writer of the “Kingsman” movies, as well as the 2011 movie “X-Men: First Class,” wrote the teleplay and will serve as the showrunner for the pilot.