Geralt's storyline in this episode is an adaptation of the short story "The Lesser Evil", contained in the collection "The Last Wish".
Of the Witcher "signs" or powers Geralt displays (at least from the games) are Axii, Aard, and Yrden.
Henry Cavill won the role of Geralt of Rivia over 200 other actors. A longtime fan of the source material, Cavill campaigned hard for the part.