Don't know who that Witcher Character is? Lets see if I can help

Clovis appears in the Hexer, episode 2 "Study", where he is in a group of three who appear to be a cohort or class, as they train together and graduate together. He snorts something, to which Geralt looks unimpressed, and Clovis tells him to Shut Up. He fails at the task of dehorsing their trainer, at which only Geralt succeeds. He mocks Geralt's more tricky way of fighting -

Avoiding - that's the way you fight. Tricks and retreat. You fight without honor, like some kind of viper.

He is dismissive and rude to Geralt, and implies he will tell the council of Geralt's subversive ideas (that they do not teach the young witchers enough about tactics).

This mockery of Geralt's "honorless" fighting is clearly projecting, when called on it (Who will tell them, you?), Clovis snatches up a hefty rock and immediately turns aggressive. When Geralt tries to calm him, speaking in a soft voice saying he had too many drugs in his system, to calm down, Clovis drops the rock and (clumsily) draws his sword. This fight is interrupted by Adela. With 2 months left until their final trials, Adela acknowledges that this is a tough time period. Clovis, however, is childishly chopping at vegetation with his sword. Adela questions the use of potions without their teacher present, but Geralt deflects it, saying they are waiting for their next teacher to arrive. Whether or not she believes him is up for debate. Either way, Geralt is polite, and clearly very curious to the women witchers. As soon as they leave, Clovis is immediately disparaging and mocking.

Bullshit. "What's your name?", "We know each other" You're an idiot. These are women. Do you know what men need them for?

He answers his question himself, by whistling and crudely thrusting his hips, making it very clear he sees them only as sexual objects. Geralt takes only a moment to stare at him before punching him in the face.

Geralt is reprimanded for his reaction to Clovis - although it is admitted that Clovis' reaction to the women was disgusting. Later, they are confronted about the fight and forbidden drinking of elixirs, which Clovis quietly admits to. He (as well as the other two) are given the punishment of "square", in which they stand on a rectangular stone for two days and two nights. They stand through the rain, and make it to the end of their punishment. Clovis collapses onto the ground. However, the episode ends with Clovis, Gascaden, and Geralt all recieving their medallions, swords, and a small bag of medicines and potions while a small speech is given.

First, a moment to introduce the Bear School: 

From The Witcher's Journal (R.Talsorian TTRPG):

The Bear School has a reputation for being huge, hefty and hairy, much like their namesake. As their founder, Arnaghad, is said to be 9 hands wide at the shoulder- not sure if that's just part of what makes up most Bears who survive the mutations or just the rumors that surround them. While the Viper school is known for its beginnings in betrayal, the Bear school's beginnings were the same. Arnaghad was the first to break the Order of Witchers. Their keep was far south; in the Amell Mountains. They were known as kinslayers, though infighting between schools was generally considered not worth it. They were estranged brothers, not bitter enemies. Gwent disagrees, however, saying meetings rarely end without bloodshed.

From Gwent: 

Their armor: Quilted gambeson, Heavy mail that extends all the way to the knees, plate armor spauldrons. It's tank armor- meant to endure blows, for melee attack. They were often found in Skellige, one even featured in the Ballad of Torgeir the Red. 

Bears were said to be loners, avoiding even those of their own school once they've grown and been released onto the path. They abandoned Haern Caduch rather than fight for it against a mob of peasants- though Gwent points out that the secrecy of its location is notable, as the slaughters of the Wolf and Cat school are infamous on the continent. It's implied (Thronebreaker) that the mutations have drastically neutralized their emotions/feelings- Possibly being why it was so easy for them to abandon the keep. 

- Ivo of Belhaven, Thronebreaker. Re: Witcher motivations Junod we mostly hear about from Ivo. Junod apparently liked the sound of Ivo's sobriquet, and decided to use it as well- becoming Junod of Belhaven. The reasoning being that Junod did not expect the smaller witcher to live very long, so 'stealing' his sobriquet wouldn't be an issue. However, it was Junod's life that was cut short. In May, 1243 Junod seached out the grandmaster smith Tyen'sail to forge him a set of the Grandmaster Ursine Armor. However, he lost all his money gambling so needed work in order to pay for it. He took a contract from Charité Gontran de Tufo, and after research headed to the caves the following day.

He carves this bear medallion on the walls, leaving the following warning:

 Warning! Buildings around here have been collapsing because a monster’s dug tunnels all over the place. Not sure yet what kind of beast it is. Don’t come after me. And don’t wipe my symbols off the walls, because I need them to find my way out.

He was ill-prepared for this fight, and regretted accepting the contract, as Geralt finds out from his journal. He did try to complete it, but fell to the Shaelmaar. In Blood and Wine, you can collect the diagrams that the fallen witcher left behind.

Junod is remembered as being as big as a mountain, with a beard that would put a Dwarf Elder to shame. He was also not one to hide his thoughts, but spoke plainly and candidly. He also apparently "haggled like a fishwife".

Gwent Flavor Text:

Rumour has it he was born of an unusual love between a lady giant and one VERY brave dwarf. Gwent Voice Lines: 

Gweld is from Zdrada. I have a fan translation which is quite good- but the translator makes a point to say they are not bilingual, and says their English poor. This is not a note to shame them- just to keep in mind while reading.) Please note that this will be full of spoilers- but I’ll be skipping most of the plot that doesn’t revolve around Gweld directly. 

The comic begins showing Gweld and Geralt training. They show trainees being injured and dying, from training, monsters, and then a fairly horrifying scene about how they won’t all survive the herbs. Gweld wakes up from a nightmare where he dreams of Geralt’s death from the herbs- it’s pretty horrific. A transition from a skull back into Geralt’s face. Geralt soothes him, and we find out about the upcoming Cat Witchers! Note: Geralt gets the top bunk. 

We find out that Vesemir agreed to a swap of trainees between the Cat and Wolf school- to learn each other’s training. Gweld is the one chosen. Vesemir sends Geralt, Gweld, Gardis and Aubry to the Cats, no fighting is allowed. One beer is. On the way they bicker and tease each other. We find out that what we’ve seen is the Wolves’ Summer Camp, not Kaer Morhen, but before Gweld has to leave... 

Gweld is ready for a fight at the Cat Witcher’s provocations, and they agree to a match only to upset the locals who think it’s an attack, as the Wolves showed up with 4 and only 3 Cats showed up. Vesemir and Guxart show up, and while they’re no love lost between them, it’s settled and they all go their own way. Gweld will return to the wolves after the tournament. 

There’s a little bit of politics in the background that differ from other canons here:  We find out that Radowit II the Brave is seeking info on how to destroy the witchers, who he believes are raising forces to war against him- although they rely on his money. Vesemir denies this, however, and says that the forest protects the witchers. This is confirmed by a mage, later. Radowit’s advisors blatantly lie and encourage them to starve the witchers into submission.  This is the canon that gives us Treyse as the headmaster of the Cats, and Rennes for the wolves. 

We then see the Cat witchers murdering and stealing, which find out was a setup. Guxart is suspicious, but the medallions found on the bodies were Wolf medallions.  And while Geralt’s getting laid again, Gweld has gotten a haircut and seems to be excelling at Cat Training. Guxart is impressed, though Gweld’s sparring partners don’t seem pleased. 

And after some drama, we find out that the wolves medallions are each different. Geralt has an Iron Wolf Medallion, while Gweld has Black Onyx. Geralt discovers his was lost and Rennes is there to show that both he and Gweld have been set up for the murder we saw previously. (The one Geralt was wearing was taken when he was getting laid. We find out later that Gweld allowed the Cats to take Geralt’s, as they told him they were returning it to Geralt.) 

Rennes here is willing to give both boys to Radowit, but Vesemir argues against it- apparently they’re the two best. But before anything further can happen Guxart and Vesemir are taken captive before the tournament, a joint “exam” of the schools. We quickly find out is not fairly organized. 

Kolgrim is found in W3, and Gwent.

This is one instance in which the Lore between them mostly agrees: 

Geralt can listen in on a conversation between two women doing laundry near White Orchard. One of the women's grandmother told her of how a local boy (Vitty) had gone missing. The villagers immediately suspected a witcher who was hunting nearby at the time and tried to capture him.

The witcher was resistant to the villagers and clashed a short while before one of the villagers beheaded him. Gwent says it was Paul, the father of the boy who got his revenge. Soon after the witcher's tragic death it was discovered that the missing boy was killed and eaten by a drowner; the witcher was completely innocent. His body was then buried in the local crypt. Upon locating the crypt Geralt discovers witcher's decapitated body with his skull in his lap, as well as a sword diagram and a journal where he learns of his identity. 

Kolgrim’s Journal Entry: 

To: Ivar Evil-Eye, master witcher of the Viper School. I have now found all the legendary diagrams once belonging to our order. Certain complications have arisen, however. On the way back to our keep, I stopped to rest the night in a village in the Temerian borderlands. The blasted peasants decided to make me into their scapegoat and accused me of kidnapping some beekeeper's brat. They took me into the local lordling's castle for interrogation, during which they found and confiscated one of the diagrams. But do not fear, I will get it back. They did not find the others. I have invoked Temerian common law and demanded a trial by ordeal instead of submitting to the whims of this baronet. My request was granted and tomorrow I am to cleanse the baronet's family crypt of wraiths. I expect this will prove little trouble. Perhaps I will already have returned to our keep by the time you receive this letter. Light the furnances -we'll have some forging to do. Kolgrim

Interrogation Report: Location: Amavet fortress Persons taking part: Sir Ignatius Verrieres, Bart., the bailiff Andreas Blume, Sir Ignatius' underlings: Carmy, Gardy and Bellsy. Suspect: Kolgrim, witcher of the Viper School.

The witcher Kolgrim stands accused of kidnapping Vitty, son of Paul, a beekeeper residing in White orchard. Suspect was detained pending trial. Upon detention he was searched and a diagram for the forging of a steel sword was found on his person. it is suspected this sword was used to intimidate or possibly kill the kidnapped child. It is likewise suspected that the accused possesses other such diagrams for the forging of death-dealing implements, though none have been found to date. Sir ignatius has requested the witcher undergo preliminary interrogation with the application of torture.This will take place once a torturer with the proper qualifications has been found.Addendum:It was later discovered Drowners were responsible for the boy's disappearance. Unfortunately Kolgrim died before this information reached the investigators, for rather than face the baronet's judgment, he chose trial by ordeal. Sir Ignatius agreed and ordered he cleanse the Verrieres family crypt of specters. Kolgrim never emerged from said crypt. It is highly likely the motley wraiths, specters and evil powers residing therein proved too much for him.

Artist:  Anton Nazarenko His Reward Tree Lore: Scroll 1: Fate seemed to take pleasure in torturing Kolgrim. Fortune only smiled upon him if it was accompanied by a stroke of very bad luck. It was always thus, even before Kolgrim became a witcher. When he was still a young harmless brat... Scroll 2: On the eve of Saovine small Kolgrim was kidnapped by a weeper, which replaced him with its own cursed offspring. Fortunately, the monster was slaughtered by a witcher that very same night. The boy's savior, having taken pity on him, decided to escort him back home. Kolgrim was relieved to be returning to the warmth and safety of his mother, unaware of his impending misfortune. Scroll 3: The woman greeted the witcher with hatred in her eyes, not believing a single word that came out of his mouth. Blinded by her contempt, she refused to even look twice at her own crying son, utterly convinced that the weeper's baby was her real child. With the door slammed shut in their face, the witcher had no other choice than to take Kolgrim with him – straight to the Viper School. Scroll 4: Over many future years, fate mocked Kolgrim many times – both during his murderous training and the later travels around the Continent. His life ended most ironically. For he, who was once stolen and then rejected from his mother, was accused of kidnapping a child. Chest 1: When master Ivar Evil-Eye instructed Kolgrim to look for the lost weapon diagrams that once belonged to their order, bad luck struck again. Although the witcher managed to find the legendary diagrams, he never returned to their keep. In the small village of White Orchard, Kolgrim was accused of kidnapping the beekeeper's son. The local baronet, wishing to appease the enraged people, called for a qualified torturer. Justice would be served, no matter what. Their justice, of course, so in response Kolgrim invoked Temerian common law, demanding a trial by ordeal. Surprisingly, the baronet agreed and ordered the witcher to cleanse his family crypt of wraiths. According to official sources, Kolgrim perished in the attempt. Yet rumors claimed otherwise. Some locals, enraged by the lordling's decision, supposedly attacked the witcher before he even entered the crypt. The beekeeper had taken his rightful revenge, cutting the mutant's head off with his own hands... Well, 'twas just a rumor. But one thing became clear over time. It was drowners that killed the missing boy. Not Kolgrim.

Kolgrim’s Gwent Card Flavor Text: 

Fortune only smiled upon him if it was accompanied by a stroke of very bad luck.

Kolgrim’s Voice Lines

Justice in this world? Not an ounce of it.

Lady Fortune can be a cruel mistress.

To clear my name and restore my freedom, I will serve.

I demand justice- a trial by ordeal.

Gezras of Leyda is a Gwent-only witcher. 

His Reward tree lore: 

Scroll 1: Gezras, born a half-elf, was considered an abomination and sold to the mages of Stygga castle at a very young age. His mutations were part of a new process designed to dull the emotions of would-be witchers even more than usual. The new recipe, however, failed… spectacularly so. Instead of inhibiting emotions, the method⁠—quite ironically⁠—enhanced them, leaving Gezras and his new brothers permanently unhinged and prone to erratic behaviour. Scroll 2: More concerned with discovering the source of their error than the well-being of their test subjects, the mages caged their spoiled batch with the determination to dissect until a solution could be derived. Upon waking in a pile of discarded corpses, barely alive, Gezras was able to crawl out and free his remaining imprisoned brothers. Together, they somehow managed to escape into the night before the mages' labour could resume. Scroll 3: Over the next few years, they found refuge among the Aen Seidhe, who helped them hide from those still seeking to abolish their past mistakes. In exchange for their sanctuary, they used their skills to engage in guerilla warfare and assassinations on behalf of the elves. Scroll 4: Having grown in numbers and strength, the Feline witchers set forth to infiltrate the quarters of their misguided creators, slaughtering them as they slumbered. Their vengeance finally sated, Gezras led his newly-formed School of the Cat north where, free from their mired past, they could start anew. Chest: The Witcher School of the Cat did not have one specific home. Over the years, there were numerous hiding places in which witchers subjected their adepts to mutations. They created numerous camps where they trained together. Nevertheless, the founder of the Cats was indeed “created” in Stygga Castle, and thus—it was their first home. Not for long, however. In rebellion against those who created them, young Gezras led other witchers to escape the castle. Needless to say, they had to earn their freedom by force. After the painful experiments they were subjected to, many were more than eager to bleed the mages that had wronged them. Later, the Cats grew stronger, bolstering their ranks with badly mutated witchers who had been rejected by other schools. The outcasts gathered together to raise the next generations through corrupt experimental methods. Over time, their warped mutations and aggressive disposition earned them the disdain of other schools.

Artist: Bogdan Rezunenko

Gezras’s Gwent Card Flavor Text: 

“Take a contract from Aen Seidhe over a dh'oine any day, as you’re far less likely to receive a knife between the ribs in place of coin.” ⁠— Gezras

Gezras Voice Lines

To play with my prey- I enjoy that the most.

Hush little Monster... Don’t growl a word. 

We didn’t taint the mutation process. We improved it. 

No point in showing mercy. No point at all.

There’s a great deal to be learned from the Aen Saevherne. 

(Aen Saevherne are not just ‘elven mages/magic users’. They are more like sages- extremely well learned and respected, some of the most powerful.)