Yennefer of Vengerberg (born in Belleteyn in the year 1173) is a sorceress who comes from the capital of Aedirn, Vengerberg. She is the youngest member of the Loggia delle Maghe and the great love of Geralt of Rivia. For Ciri she is a maternal figure, as well as a guide and mentor.

The "Lady of Vengerberg" was famous for her beauty. During the events in the book La Torre della Rondine she is said to be 94 years old. Yennefer always wears black and white, has purple eyes and raven and curly hair, and wears a star-shaped obsidian jewel around his neck, tied with a black velvet ribbon. Wherever she goes he always carries with him the scent of lilac and gooseberry. Yennefer has a quarter of elven blood in her genealogy, which makes her a quarteron.

The sorceress has a decidedly fickle, capricious and stubborn character. The relationship she has with Geralt of Rivia is in fact terribly stormy, made up of often furious quarrels and long periods of distance between the two. Finally the couple marries in an equally lively ceremony, according to the events described in the story Something ends, something begins.

During the Battle of Sodden Hill, Yennefer was blinded by Fringilla Vigo, a Nilfgaardian sorceress. His vision, however, was restored thanks to the magic.

Like many other sorceresses, Yennefer is also sterile, and this condition weighs on her to the point of looking each time for a different way to change her condition. In the story The Last Wish, Yennefer tries to trap a dangerous genius in order to take advantage of the desires; in the tale The limit of the possible, Yennefer participates in the hunt for the dragon to take over the parts of the beast, hoping to create a spell that will heal her from infertility. In The Voice of Reason, the frame story of the Guardian of the Innocents collection, Geralt gives the priestess Nenneke a bag with precious gems, which she received as payment from King Foltest, after breaking the spell of the striga that was the victim of the daughter. Geralt tells Nenneke that Yennefer would never accept it from her hands because she is too proud, but the care and research to solve the problem of infertility, which is so dear to her, is very expensive. Subsequently, when Yennefer meets little Ciri, she takes care of her with great dedication and maternal affection, becoming in fact the loving mother that the child has not had.

Like most of his fellow magicians, Yennefer was not beautiful by nature. In the story "The Last Wish", Geralt discovers that Yennefer has changed his appearance thanks to magic, but that initially he must have been an unfortunate like many others:

" All tastes are tastes, but in fact few were the magicians to call them" beautiful ". They all came from social circles where the only fate of girls was marriage. Who would have thought of condemning a girl to years of strenuous study and to the torture of somatic changes, when it was possible to marry her and make an advantageous relationship? Who would have wished to have a sorceress at home? [...] Therefore only daughters who had no chance of finding a husband became magicians. Unlike the priestesses and druids, who unwillingly accepted ugly or crippled girls, the wizards welcomed among them whoever leaked a predisposition. If then the girl passed the selection of the first years of apprenticeship, the magic intervened, straightening and leveling legs, adjusting badly grown bones, accommodating cleft lips. By removing scars, birthmarks and traces of smallpox, the young sorceress became "attractive", because it required the prestige of her profession. The result was pseudo-beautiful women with bad and cold eyes from ugly women. "
- pp. 314, "The last wish", included in The Guardian of the Innocents

“ And Geralt suddenly knew the truth. He knew who had been once. What he remembered, what he couldn't forget, what he lived with. Who was actually before becoming a sorceress.
Because looking at him were the cold, piercing, bad and wise eyes of a hump. "
- pp. 353, "The Last Wish", included in The Guardian of the Innocents

Yennefer was also the adviser to King Demawend of Aedirn and a friend of Triss Merigold. At the end of the Witcher saga, she will almost give his life trying to save that of his great love, Geralt, in the book The Lady of the Lake.