The Witcher books
Andrzej Sapkowski is a Polish author who created The Witcher (Wiedzmin) book series, beginning with the short story "The Witcher" in 1986. The series includes two short story collections (The Last Wish, Sword of Destiny) and five novels (Blood of Elves, Time of Contempt, Baptism of Fire, The Tower of the Swallow, The Lady of the Lake), plus a standalone prequel (Season of Storms).
The books established the entire world that CD Projekt Red's games are built on: the Continent, the witchers, the Elder Blood gene, Ciri, Geralt, Yennefer, and the political landscape of the Northern Kingdoms.
Relationship with CDPR
Sapkowski initially sold the game adaptation rights to CD Projekt Red for a lump sum, reportedly underestimating the games' commercial potential. In October 2018, he demanded additional compensation (at least 6% of profits) under Polish copyright law. The dispute was resolved with a new agreement that is reportedly favorable to both parties.

Despite the improved financial arrangement, Sapkowski has minimal creative involvement with the games. He has stated: "There is no cooperation at all between me and the games." Requests from CDPR for advice are "a great rarity" and he knows "practically nothing" about The Witcher IV beyond general information like Ciri being the main character.
Views on The Witcher IV
Sapkowski was not consulted about the decision to make Ciri a witcher who has undergone the Trial of the Grasses in The Witcher IV, a departure from the novels where Ciri never underwent the Trial.
He has no plans to play the game: "It's not an entertainment for me." On his current relationship with CDPR: "The contracts between me and the game people are excellent right now. Let's hope it stays that way."