Though Geralt of Rivia can not be defeated by many characters, his body still has its strengths and weaknesses. Besides, he has done some things that are quite morally questionable—just like pretty much everyone else on the show.
But what is really interesting is how these characters can be classified according to their personalities, actions, decisions, and words. Here's how we think The Witcher's characters would fit in Harry Potter's Hogwarts.
Istredd: Hufflepuff
In a world like the one in The Witcher, it is a mystery that a character like Istredd was able to survive for so long. The book, the game, and then the series presents a dark version of our world sometime in the Middle Ages, which means that there is a lot of violence and the living conditions are not the best, so to say.
Istredd is most definitely a Hufflepuff. Even though he is quite intelligent, which could signal that he is a Ravenclaw, his kind nature and friendliness are both characteristics that Hufflepuffs possess. Besides, he treats Yennefer well, even after she practically broke his heart.
Dara: Hufflepuff
Just like Istredd, Dara shows friendliness and kindness. Even though this is only towards his new friend Ciri, it does extend to the dryads afterward. That being said, Dara is very cautious and doesn't approach anyone "just like that," which still makes him a Hufflepuff.
Unlike many other characters from the series, Dara seems to show traits only of one of the four Hogwarts houses rather than combining several. Of course, you could argue that his cautious nature comes from his intellect which could signal that he is a Ravenclaw, but that is still not as prominent as his Hufflepuff traits.
Mousesack: Ravenclaw
Mousesack is undoubtedly one of the most likable characters on the show. He is smart, is capable of magic, and has a great sense of fashion. In addition to that, he is also one of Geralt's closest and oldest friends, which is clearly noticeable by the way they treat each other with respect and fondness.
Considering his sharp intellect and extensive knowledge of magic, Mousesack is most definitely a Ravenclaw. He could be a Slytherin or a Gryffindor because of how he acts in some situations, but he is still mostly a Ravenclaw no matter which scene you want to look at.
Tissaia de Vries: Slytherin
Tissaia de Vries is probably one of the most ambitious characters in the whole series (the only character more ambitious than her is probably Yennefer). The majority of the audience probably hates Tissaia, but she can still be admired for some of her traits and even likable in some situations.
Consequently, most of Tissaia's actions, decisions, and words indicate that she is a Slytherin. She aspires to achieve a lot and stays loyal to her duty. At the same time, she is not afraid to hurt others or be strict towards the young women she teaches and prepares to become some kind of version of her one day.
Cahir: Slytherin
A clear antagonist in Ciri's storyline, Cahir appears to display very similar traits to the ones Tissaia de Vries has. We don't see much of him, but we do get enough scenes where he makes decisions and acts in some way that helps to understand what kind of person he really is.
Cahir is not afraid to do evil deeds to achieve whatever he has set out to achieve. He deceives people, manipulates them (sometimes manipulates them into manipulating others), kills without mercy, and keeps looking for a way to do whatever it takes to capture Ciri and conqueror lands. This, ultimately, makes him a Slytherin.
Fringilla Vigo: Slytherin
Fringilla Vigo is known for being an extremely powerful sorceress, but what she is also known for is taking the side of Nilfgaard rather than siding with her fellow sorcerers and sorceresses. In fact, she even actively fights with her past allies in order to help the Nilfgaardian army.
Fringilla is most obviously a Slytherin. She does have an inquisitive mind and can find smart solutions to the problems she encounters, but she is also quite ambitious and loyal to her "new" allies—Nilfgaard. She is loyal, but not to the ones who she used to be loyal to.
Jaskier: Hufflepuff
Perhaps one of the most beloved characters in the entire show, Jaskier is a close friend of Geralt. Though we didn't see much development of their relationship in the show, the book makes them become really good friends. Nonetheless, what is more interesting is Jaskier's personality.
He is obviously a true Hufflepuff. He is the ultimate goofball of the series having that lighthearted, happy-go-lucky attitude to life. He sticks to Geralt and genuinely loves him, but he is also very friendly—sometimes too friendly—toward strangers. As a result, he is the quintessential Hufflepuff.
Ciri: Ravenclaw
It might come as a surprise that Ciri is actually much older throughout the majority of the books, as we only see her as a child in the show. Consequently, we will probably see her as an adult in future seasons, which will definitely be just as exciting.
She is brave, she loves her family and her people, and she is quite friendly—all of these could easily place her in Gryffindor, Slytherin, or Hufflepuff. But what she really stands out with is her wit. She is able to find solutions almost instantly, which does make her look more like a Ravenclaw than anyone else.
Yennefer: Slytherin
Another outstanding female character on the show, Yennefer is almost a complete opposite of Ciri in the first season of the series. Nevertheless, the two will eventually become very close and will have to work together and go on numerous adventures along with Geralt.
Considering that she takes a lot from her teacher Tissaia, Yennefer is more of a Slytherin than Tissaia is. On the other hand, Yennefer's loyalties seem to lie only in her own interests rather than a certain side or cause that she could follow. She is out for herself, and she will do anything to achieve her goals.
Geralt of Rivia: Gryffindor
Geralt of Rivia has now become an iconic character. Back when he was only in books and then when he was in the game, he was already beloved by millions, but the show (and Henry Cavill) gave him a new hoard of followers. But, even though some of his actions are questionable, he is still likable because of his personality.
Geralt is a Gryffindor. He is smart and brave, and, in difficult situations, he is strong and willing to take risks. Even though he tries to do the right thing, he doesn't always end up doing what's right, and not everyone likes him for it. A bit like Harry himself, perhaps.