A group of monster hunters who seek out and kill dangerous creatures usually for money. Raised from birth to be killers, they are commonly referred to as mutants, although their abilities are not genetic, but a result of potent mutagens they take in their training which give them enhanced reflexes, strength, and eye sight; only the strongest apprentices survive the process.
Apprentice witchers must undergo a series of trials, the most significant, and dangerous, of these trials is the Trial of the Grasses. It is this trial that gave Geralt of Riva his white hair, though not all Witchers have this trait.
As well as improved martial skills witchers also possess knowledge of alchemy and magic (specifically witcher's signs), which they make extensive use of in their quests. Potions are used to enhance their bodies in order to better combat the superhuman creatures they face. Witchers also often employ a variety of bombs against large groups or more dangerous opponents; their knowledge of alchemy can be used to make salves which enhance their blades' strengths against opponents with specific weaknesses.
Witchers signs have a variety of effects from shielding them to clouding the minds of their enemies. These signs require very little magical ability or energy to use as they just require a small, one handed gesture to summon, which is why they are favored by the monster hunters. Real magicians look down on the signs as mere child's play, but the witchers use them effectively in combat.
Witchers are very particular to disassociate themselves from bounty hunters and assassins, and take offense to those who offer contracts on humans. Due to their identifiable mutations, particularly their catlike eyes, tendency to cause trouble, and general lethality, witchers are shunned by most humans.
They carry two swords, one made of steel and one made of silver. Contrary to popular belief, both can be used on monsters as some creatures react differently to each metal, although creatures do tend to be more susceptible to silver.
All witchers wear medallions which are sensitive to magic, and vibrate when magical elements are nearby. The medallions also signify which school the wticher was trained in. There are evidently multiple schools of Witchers, Geralt belongs to the Wolf School of Kaer Morhen, and Letho is shown to be a member of the Viper school. The Cat and Griffin school's are both mentioned in Andrzej Sapkowski's original novels.
There is also no reference to female witchers, whether this means there are none, or simply that we haven't seen any is unknown. There are very few witchers left in the world due in part to the decreasing number of monsters. It is likely that once all the monsters are gone witchers will soon follow. The majority of witchers were killed at Khaer Morhen, by a mob of religious fanatics and wizards led by Azar Javed. No new witchers have been created in over 25 years, and the knowledge of how to create new ones is known only in theory.
Geralt of Rivia: The protagonist of The Witcher series. Geralt is often known as the the White Wolf (or Dwynbleidd by the Elder tongue) for his solitary and taciturn nature and albino white hair. Geralt lost his memory in an incident before The Witcher and spends a good portion of the games struggling with amnesia and trying to find out what happened to him.
Vesemir: The oldest and most experienced of the witchers at Kaer Morhen, Vesemir is viewed as something of a father figure by the other witchers.
Leo: A young witcher who dies when Salamndra attack Kaer Morhen at the start of The Witcher. Leo was not a true witcher as he had not yet undergone the witcher trials and taken the mutagens that enhance witcher strength and reflexes.
Lambert: One of the younger witchers at Kaer Morhen. Lambert has a sharp tongue especially when directed towards Triss Merigold, whom he sees to dislike, although he is very concerned for her when she is injured at the beginning of The Witcher.
Eskel: Eskel is distinguished by a disfiguring scar across his face. After curing Triss in the prologue of The Witcher Geralt can receive a fistfighting tutorial from Eskel, along with some more general tips about fighting.
Berengar: Berengar resents the witchers for denying him a normal life. In Geralt's quest to track down Salamandra and recover the mutagens stolen from Kaer Morhen, he tries to find the witcher Berengar who was mentioned to him by Vesemir. At first Geralt is led to believe Berengar is dead, but eventually finds him alive and is challenged to a duel by him. Should Geralt spare him Berengar joins in the fight against Azar Javed and is slain.
Letho of Gulet: A witcher from the Viper school. Letho is responsible for the assassination of King Foltest at the beginning of The Witcher 2: Assassins of Kings and plans to kill all the kings of the Northern Kingdoms, recruiting Iorveth and the Scoia'tael to aid him in this mission (although he later betrays them). Letho bests Geralt in a battle, but spares him as Geralt once saved his life. The player can choose to kill Letho at the end of The Witcher 2.
Auckes and Serrit: Two witchers of the Viper school working with Letho. Geralt first encounters them when they attempt to assassinate King Henselt of Kaedwen.