Geralt of Rivia (/ˈɡɛr.əld/, GHERR-əld; Polish: Geralt z Rivii) is a fictional character and the protagonist of The Witcher series of short stories and novels by Polish author Andrzej Sapkowski. He is a magically enhanced monster-hunter known as a "witcher", who possesses supernatural abilities due to his mutations.

Geralt of Rivia is also the protagonist of CD Projekt Red's series of video games based on The Witcher. In television adaptations, he was portrayed by Michał Żebrowski in The Hexer film and television series. Henry Cavill portrays the character in the first three seasons of Netflix's The Witcher television series, with Tristan Ruggeri portraying a young Geralt in the first season, and Liam Hemsworth due to take over the role from the fourth season onward.

Geralt is a witcher, a magical mutant made for hunting and killing monsters. Shortly after being born, Geralt's mother, Visenna, gives him away to undergo training and, eventually, become a witcher at the School of the Wolf at Kaer Morhen – the stronghold of the Wolven school witchers. His mentor and father figure there was a wise man and warrior named Vesemir. Geralt survives mutations during the Trial of the Grasses, thanks to which he gains various witcher traits: high resistance to injury, poison, and diseases, as well as slowed aging. Uniquely, Geralt had an unusual tolerance for the trials and was subjected to experimental mutagens as a result. Due to this, it caused the loss of all body pigmentation, leaving him with pale skin and white hair, which is the reason why he is referred to as Gwynbleidd in the Elder speech (close to the Welsh translation "Blaidd Gwyn"), meaning "The White Wolf".

Despite his name, Geralt does not come from Rivia. Geralt received his training as a witcher in Kaer Morhen, which is located in Kaedwen; this is where he may actually be from. He added "of Rivia" to his name as he began work as a witcher, under advice from Vesemir that folk would be more trusting of him if he had a surname. Years later, he helped Queen Meve of Lyria and Rivia during an important battle, after which she knighted him, officially bestowing on him the title Geralt of Rivia.

After completing his witcher training, he receives his Wolf medallion (the symbol of Kaer Morhen) and embarks into the world on his horse called Płotka (literally, "Roach" ; he gives the same name to every horse he owns) to become a monster slayer for hire.

I looked for the words "Witcher urgently needed". And then there'd be a sacred site, a dungeon, necropolis or ruins, forest ravine or grotto hidden in the mountains, full of bones and stinking carcasses. Some creatures which lived to kill, out of hunger, for pleasure, or invoked by some sick will. A manticore, wyvern, fogler, aeschna, ilyocoris, chimera, leshy, vampire, ghoul, graveir, were-wolf, giant scorpion, striga, black annis, kikimora, vypper... so many I've killed.

— Geralt, in Andrzej Sapkowski, The Last Wish, "The Voice of Reason 4"

Even though Geralt does not believe in destiny, he unknowingly demands the unborn child of princess Pavetta and her husband Duny as a reward for his services by invoking "the Law of Surprise". The child turns out to be a girl, Cirilla, commonly known as Ciri; since then the two are linked to each other. At first, Geralt does not take her because traditionally women were not witchers. However, fate causes Geralt and Ciri to cross their paths twice, with him claiming her for a second time when he invokes the Law of Surprise on a traveling merchant he saves from monsters during a random encounter. Geralt ends up taking the girl into his care, becoming her mentor, training and loving her as his own daughter.