The Witcher series has appeared in many different forms. From tabletop RPG to a show on Netflix, the stories and characters set in this universe are compelling enough to warrant retellings and variants of all kinds. The two versions that most people are familiar with are the games and books, though there are stark differences between the two.
There are many drastic changes that took place as the various elements of the novels were incorporated into the video games, the most notable being what happened to the characters in regards to their personalities, motivations, as well as their actions.
10 Regis
In The Witcher 3's Blood and Wine DLC, Geralt will encounter a few powerful vampires. The two most important being Regis and Dettlaff, higher vampires from the Gharasham tribe. Throughout the events of the story, Regis proves not only to be wise, but compassionate. Though, in the books, he proves that monsters can be even more altruistic than this. There's a part in the books where an antagonistic mage named Vilgefortz attempts to kill Yennefer, but Regis heroically sacrificed himself to save her, which resulted in him burning to death.
9 King Foltest
Foltest is the monarch most seen in the series and he is usually portrayed in a positive light. Especially when compared to rulers of other lands. Calm, logically, and kind, he seems like the perfect king. At least, in the games. In the books, he is seen as more controversial in regard to his politics and decisions. In a governmental landscape where witchers-turned-assassins could be lurking in the shadows, this is not a good reputation to have.
8 Fringilla Vigo
An associate of Yennefer's from the Lodge, and once one of Geralt's lovers, this Nilfgaardian sorceress plays a key role in some quests in The Witcher 3, but that's about it. In the books, she aids Yennefer in finding Ciri during a crucial period for the white-haired youth. There are also a lot more descriptions of the relationship and history of the two raven-headed magic users.
7 Emhyr
The cold and calculating ruler of the Nilfgaardian Empire and father of Ciri. His unyielding manner and blunt stubbornness make him unlikeable, yet due to his position and power he cannot be ignored. The games portray him in a far more one-dimensional way in that he only cares about Ciri for his own gains.
But in the books, he ends up making a surprising decision when considering her future. One that foils his own plans because, due to some of Geralt's words, he sees the hideous flaw in them.
6 Roach
Everyone's favorite game-breaking horse and Geralt's greatest ally. This wondrous equine helps the witcher travel any location and always comes when called. The epitome of the faithful steed, their brown fur and eyes can always be seen accompanying the White Wolf on his hunts. Though, in the novels, Roach is not a single horse. But any and all horses Geralt so declares. For 'Roach' is less of a name and more of a title for whichever becomes the witcher's mount.
5 Dandelion
The charismatic bard of bright disposition is a character the player sees, and hears, a lot from. Appearing as both narrator and character, his take on the happenings of the Northern Realms are ingrained in the storytelling of the series. He tends to come off as a bit dim-witted and cowardly at times, though his book counterpart does not. Jaskier, as he is known in the novels, appears as more of a conscience-become-human for Geralt and offers sagely advice and lends a constant ear to the witcher's worries.
4 Triss
This sorceress is arguably the character that seen the most changes from her appearance in the books. In the games, she is a vibrant red-headed, green-eyed woman with an extroverted, yet conflicted nature. Her image and personality are iconic to the franchise, appearing in every game in the trilogy, but her role was immensely smaller before CD Projekt Red had a say on the matter.
In the novels, not only does she have duller hair and blue eyes, but she also has significantly fewer appearances and doesn't come anywhere close to being Yennefer's romantic rival.
3 Yennefer
Yennefer's appearance and personality are more similar to her book's counterpart than other characters, but there are still some key differences. In The Witcher 3, she comes off as a flawless beauty of intimidating magical might. The book version of this sorceress tends to give off more witty and shrewd vibes than effortless and elegant, though still as beautiful. In fact, likely more so.
2 Ciri
The ashen-haired young woman and pseudo-adopted child of Geralt and Yennefer visually is unchanged from the books, but her personality is not. In the games, she is seen as a bit of a hellion in her youth, causing Geralt, Vesemir, and Yennefer headaches on occasion while raising her. Her character, story, and dialogue are more light-hearted and there is no mention of the dark tale behind how she got her wicked scar. In the novels, she is a fair bit more concerned with her hatred of those that have wronged her and the desire for vengeance.
1 Geralt
No character has been changed more than the White Wolf himself. In the games, he is tremendously powerful, ruggedly handsome, stoic, confident, and never without a witty quip at the best times. He also has plenty of work, food, and lodgings available to him. These are all incredibly different from the Geralt of Rivia of Sapkowski's written adventure. In the novels, Geralt is thin and constantly on the verge of starving due to monster hunting paying very poorly and being in short supply. He is also described as being significantly less attractive, sulky, and emotionally vulnerable. He is still a mighty monster slayer but is not nearly as strong as he is when controlled by the player.