Geralt of Rivia is the main protagonist of the Witcher franchise. He is a witcher, a magically-enhanced mutant who slays monsters for a price, and the adopted father of Ciri. Despite the fact that witchers have a reputation for being heartless and the mutations are meant to kill emotions, Geralt still has a conscience and generally helps others because it's the right thing rather than to get paid, though he rarely goes out of his way to admit this.
Despite his name, Geralt does not come from Rivia: he grew up in the witchers' keep of Kaer Morhen in the realm of Kaedwen. In the interest of appearing more trustworthy to potential clients, young witchers were encouraged to make up surnames for themselves by master Vesemir. As his first choice, Geralt chose "Geralt Roger Eric du Haute-Bellegarde", but this choice was dismissed by Vesemir as silly and pretentious, so "Geralt" was all that remained of his chosen name. "Of Rivia" was a more practical alternative, and Geralt even went so far as to adopt a Rivian accent to appear more authentic.
Geralt has a soft spot for the common man, though. Content he is to watch some Earl be killed over petty land disputes, but he has a real big problem when it comes to letting the little guy get kicked around. This is usually the source of all his political discomfort, but it's earned him many great and loyal friends like the bard Dandelion or sorceress/sometimes lover Triss Merigold. These are friends who stuck by him even after his apparent death at the hands of an angry mob after attempting to defend a group of non-humans from a hate-fueled slaughter.
Geralt was the son of sorceress Visenna and (presumably) a warrior called Korin. Shortly after being born, Geralt was taken by his mother to the Wolf School - Kaer Morhen stronghold (from Elder Speech Caer a'Muirehen meaning "Fortress of the Old Sea"). Geralt survived numerous mutations during the Trial of the Grasses, through which he gained practically superhuman physical and mental abilities (increased reflexes, speed, strength and enhanced hearing) surprisingly well.
Because of that, as one of the few he was selected for additional experiments, and of the few he was the only one that survived. His white hair, completely lacking pigment, is a side effect of these experiments. After finishing the witcher training, he embarked into the world on his horse called "Roach" (he gave the same name to every one of his horses) to become a monster slayer for hire.
Although Geralt did not believe in destiny, he demanded the unborn child of princess Pavetta and her husband Duny as a reward for his services. As the child turned out to be a girl, he did not take her. However, fate or blind chance caused Geralt and Ciri, the daughter of Duny and Pavetta to cross paths thrice, and after the death of her grandmother, queen Calanthe, Geralt ended up taking care of the girl and loving her as his own daughter. His best friend was Dandelion the bard, while his lover and the love of his life was Yennefer.
Dandelion the Bard
Dandelion is one of Geralt's closest friends and has travelled with the Witcher on several occasions, some times followed by the third member of their party, Zoltan. Although the bard thinks highly of the Witcher he rarely expresses it in public, primarily due to the fact that he himself is a man of peculiar reputation and fears that his involvement with the notorious hunter of monsters would garner him the hatred and spite of powerful indiviuals and that of the general public.
Triss Merigold
Triss Merigold of Maribor was a legendary Temerian sorceress of the 13th century. She was friends with Yennefer and the witcher Geralt of Rivia, but also unhappily in love with the latter. Triss took care of Ciri at Kaer Morhen for some time and is like an older sister to her. She was also quite a powerful mage, certainly when it counted most. She wore an amulet - sapphire overlaid with silver.
Yennefer of Vengerberg
Yennefer, born on Belleteyn in 1173, was a sorceress who lived in Vengerberg, the capital city of Aedirn. She was Geralt of Rivia's true love and a mother figure to Ciri, whom she viewed like a daughter to the point that she did everything she could to rescue the girl and keep her from harm. She helped advise King Demavend of Aedirn, a close friend of Triss Merigold, and the youngest member of the Supreme Council of Sorcerers within the Brotherhood of Sorcerers.