In Andrzej Sapkowski’s fantasy novel The Last Wish, the central monster hunter is Geralt of Rivia.
Geralt is a witcher, a professional monster slayer trained from childhood and altered through dangerous mutations. The Last Wish is a collection of linked short stories rather than a conventional single linear novel, and Geralt appears throughout its episodes as the viewpoint character.
Although he is called Geralt of Rivia, he was not actually born in the kingdom of Rivia. He adopted the title because it sounded more respectable and useful when dealing with clients. The book also introduces or develops major figures such as Yennefer and Dandelion, but neither is the central witcher protagonist.