Elden Ring has been strongly anticipated by fans since 2019, when it was announced; part of the intrigue behind the game came from the involvement of George R.R. Martin, one of the most famous fantasy authors in the world. Elden Ring’s director, Hidetaka Miyazaki, was a fan of Martin’s work prior to working with him, particularly of Fevre Dream, a standalone novel that Miyazaki considered a masterpiece.
Only a couple of years before the announcement of Martin’s work with Miyazaki, Torment: Tides of Numenera released, featuring writing by another famous fantasy author, Patrick Rothfuss. (Rothfuss had been a big fan of the classic Planescape: Torment, a role-playing game renowned for its narrative.)
My own favourite example of a prose author writing for games is most likely Kiyoshi Shigematsu’s skilful work on Lost Odyssey, but you can go as far back as 1995 to find that Harlan Ellison wrote for the game adaptation of his short story I Have No Mouth and I Must Scream.
The fantasy author Chris Wooding is part of this tradition of prose writers crossing into games writing; he worked on the recent Assassin’s Creed Valhalla. But when I catch up with him he tells me that his interest in games began many years beforehand.