Sometime during Falka's infamous rebellion, Stregobor got caught up in the conflict and witnessed firsthand the destruction it caused on the mages at Mirthe. Stregobor, while he survived the rebellion, lost both his hands in a fire, leaving behind charred stumps where his hands once were. As a result, he resorted to illusions to make it look like he still had hands and to hide the injuries.
Sometime later, he became one of the heads of the Brotherhood of Sorcerers and by 1206, was the rector at Ban Ard Academy, where he became a mentor to Istredd. This turned out to be fruitful for Stregobor as, Istredd, not realizing how much his mentor depised elves and mixed people, revealed to Stregobor that Yennefer was a quarter-elf, a secret she had closely guarded. In turn, Stregobor revealed this information to the rest of the Brotherhood to deny assigning Yennefer as Aedirn's mage advisor when she was set to graduate in 1210 and instead assign her to Nilfgaard. However, Yennefer managed to get back the position that was promised to her anyways, much to Stregobor's annoyance.
Dealing with Renfri
Stregobor was a staunch believer in the Curse of the Black Sun, which was said to mark the imminent return of Lilit — the demon goddess of the night — whose sole purpose was to exterminate the human species. Lilit's path was to be prepared by 60 women wearing gold crowns, who would fill the river valleys with blood. So when an eclipse occurred in 1213 under which numerous girls were born, the mage studied them and tried to "cure" them by locking them in towers for safe keeping to run trials on, but each girl died under his tortuous experiments. This didn't deter Stregobor though, as he believed eliminating them was the lesser evil.
Most notably, he personally delivered Creyden's princess, Renfri, in the middle of the afternoon, under the Black Sun and knew for certain that she was the bringer of evil. In fear of Lilit's return, Stregobor tried to conduct experiments on her as child before eventually deciding she was too dangerous and dispatched someone to follow Renfri into the woods and kill her. However, they later found the henchman in the brush with Renfri's broach jammed in his ear. She disappeared shortly thereafter and didn't reappear for another two years. Fearing for his life and having realized Refri was now resistant to magic, Stregobor fled Creyden as she chased after him, seeking justice for what he did to her.
By 1231, Stregobor was hiding in the town of Blaviken, caught in a stalemate with Renfri who had tracked him down there with her own gang. Trying to find a way to have Renfri dealt with, Stregobor lured the witcher, Geralt of Rivia, to Blaviken with the help of his servant, Marilka, to hire him to assassinate Renfri. Stregobor explained his reasoning behind wanting to kill Renfri, regarding his belief in the Curse of the Black Sun and that it was for the "lesser evil" and what he did was justified to the girls and that Renfri wanted him dead for revenge. Despite Stregobor's offer and reasoning, Geralt noted he only killed monsters, and refused.
Despite refusing Stregobor's offer, Geralt was eventually forced into a fight with Renfri, killing her as a result. Stregobor came down to see the destruction left in her wake, and he ordered Marilka to bring him a cart so that they could take Renfri's corpse back to the tower for an autopsy but Geralt objected. Stregobor then tried to persuade the witcher that it was Renfri's mutation that allowed her to influence her followers. When Geralt refused to lower his sword, Stregobor realized that he must've been similarly influenced and directed attention to the men Geralt killed. This caused the townspeople, Marilka included, to revolt against Geralt. They threw stones at him, as Renfri predicted they would, until he left.
Conclave of Northern Mages
Stregobor was among many mages to attend the conclave at Aretuza. He, Artorius, and Tissaia led the conclave. Artorius and Stregobor had no desire to go to war with Nilfgaard. Especially not for Cintra, who rejected their mages for decades. However, Vilgefortz worried that more kingdoms would fall after Cintra as Nilfgaard wanted the entire continent. Rather than watching them fall, Tissaia wanted to help Cintra defeat Nilfgaard by convincing the kings to send their armies because if they didn't stop Nilfgaard now, more kingdoms would fall.
Fringilla arrived at the conclave and denounced any suspicion that Nilfgaard was planning to take over the continent. Under their new leader, Emperor Emhyr var Emreis, Nilfgaard had strengthened trade and funded research. Fringilla believed that in taking Cintra, they had a chance of saving the continent. If the Northern mages wouldn't take sides, Fringilla asked that they at least stay out her way. Fringilla then pointed out that if not for Yennefer, she never would've been assigned to Nilfgaard, and it wouldn't be the empire it is today. Artorius joked that had they sent Yennefer to Nilfgaard as planned, It would still be a "shitty backwater." Yennefer admitted this was true. Instead of Nilfgaard, she went to a prized kingdom and did "fuck all for decades." She helped murderers and rapists keep their crown. If given an option, she'd vote to burn it all down. The mages put it to a vote. Unfortunately, most side with Stregobor and Artorius to allow Cintra to fend for themselves.
Stregobor taught a class and told the tale of Falka, who was allegedly a power-hungry mutt of a girl who cried, "Death to all kings!" when Vridank spurned her elven mother. Bent on revenge, she slaughtered nobility, preyed on foolish followers, and incited rebellion to burn cities into the ground. All in the effort to reclaim power, though Istredd claimed this was false and that Falka was a girl forgotten by her family. She was trying to rightly recover her throne, but Stregobor pointed out that she was quarter elven just like Yennefer, and as they all knew, history had a way of repeating itself. Stregobor also claimed that he was there when Falka destroyed Mirthe and all the mages in it. Her violence etched in the stumps of his hands. Stregobor simply wanted to protect their institution from similar corruption.
After learning that Yennefer was alive and that she had returned to Aretuza a month after the Battle of Sodden Hill, Stregobor bound her to a chair and tortured her for answers, as he didn't trust her considering she was of elven blood and mysteriously went missing after the battle. When she admitted to being a prisoner of war and having been taken by Nilfgaard, he decided to dig further through her mind, but Tissaia intervened and reported him to the Brotherhood, where Stregobor reasoned that with Yennefer having survived fire magic, imprisonment by Nilfgaard and capture by elves, he didn't see it as unreasonable to suspect that she may have been turned. The Brotherhood agreed and decided to put her faith to the test by ordering Yennefer to kill Cahir, but she helped him escape instead.
Birth of an Elven Baby
Stregobor and Artorius learned from Dijkstra that an elven baby had been born of a mage in Cintra, which they saw as a potential threat, but Tissaia and Vilgefortz had no intentions to act on unfounded prejudice and rumor, to which Dijkstra replied that today's gossip is next month's news. For instance, he heard that Triss had returned, which the Brotherhood was not aware of.
- It appears that the show's Stregobor is a combination of two distinct book characters: Stregobor, a Kovirian mage who wants to prevent the Black Sun, and Gerhart of Aelle, the rector at Ban Ard Academy and one of the oldest mages of the Continent.