[Correction: As user Jan Milik points out in the comments, it's much more likely that Vávra's statement refers to Andrzej Sapkowski's Hussite Trilogy books rather than The Witcher books. It's still the author of The Witcher, just not The Witcher source material. I apologize for the mix-up.]
When Kingdom Come: Deliverance launched in February, it didn't take players long to find all the secrets scattered across its take on 15th century Bohemia. There are easter eggs from all the heavy hitters of high fantasy -- Lord of the Rings, The Elder Scrolls, Game of Thrones to name a few. However, there are Witcher references that probably sits nearer and dearer to the creators than the other ones.
For a presentation at Krakow-based Digital Dragons, Kingdom Come: Deliverance director Daniel Vávra gave a lengthy talk about historical accuracy and what kind of research Warhorse Studios did to create what it felt was the most accurate depiction of the region 600 years ago. Early into the session, Vávra switches slides to reveal a large picture of Witchercreator Andrzej Sapkowski. He's fantasy royalty in Poland. There's a brief interruption as the room breaks into applause.
Vávra explains how Sapkowski and The Witcher helped shape Kingdom Come: Deliverance. "[Sapkowski] was very important. He wrote, I would say my favorite books. It's funny that one of the best historical books about [Czech] history was written by a Polish guy," Vávra says.
He continues "But I really do think that it's really well-researched. Despite the fact that there are fantasy elements, it's one of the best books about this period of our history. It was a huge influence on me and I also learned a lot of facts from the book because it depicts the daily life very well."
Make no mistake about it: Kingdom Come leans as far into realism as it possibly can. Fantasy is the exact opposite of what Warhorse wanted to accomplish. But, it turns out Poland's most famous fantasy series is steeped in enough realism that it ended up as a notable influence for Vávra and his team.