Reidrich was a mage at Kaer Morhen and one of the last ones who knew the mutagenic secrets to create witchers. His death, along with the sacking of Kaer Morhen, led to the School of the Wolf's decline as they were no longer able to create witchers.
Biography
As a mage of the School of the Wolf, Reidrich was responsible for performing the Trial of the Grasses and investigating the monsters that the witchers brought back. Along with other mages in the settlement, he was also responsible for ensuring that the secrets of the mutant organisms were not used for improper purposes.
In 1108, after the massacre in Red Swamp, Reidrich found himself in the bestiary, where Vesemir also arrived, by accident, guided by the power of the medallion. The mage believed that a future monster hunter should know the truth about the creation of monsters like him, so he told the boy a brief history of the use of mutagenic alchemy. However, the conversation was interrupted by Deglan, irritated by Reidrich's behavior. The witcher informed the boy about the letter that awaited him, so he left the room. The same year Reidrich carried out the Trial of the Grasses with the surviving recruits including Vesemir.
In 1161, Deglan kidnapped a young elven girl, Kitsu, and ordered Reidrich to mix her genes with those of a Mahr. The population of monsters decreased year after year, so Deglan decided that to ensure the survival of the guild, new monsters must be created. However, the experiment turned out to be too unstable and she died. They had her body discarded like other failed experiments, not realizing in actuality that Kitsu had used the mahr's traits to create an illusion she'd died to escape.
In 1165, as a result of an investigation by Vesemir and Tetra, the truth about the experiment came to light, causing King Dagread to give permission to attack the fortress. Lady Zerbst went to Kaer Morhen to warn the witchers. There, she met Reidrich, and the two entered the labs to interrupt Vesemir's fight with Deglan and notify them of the threat. The four of them headed to one of the towers, from where they could see the crowd gathered under the fortress. The mage announced that Tetra cared more about him and his brothers, because without them the knowledge of creating witchers would be lost. In response, Deglan ordered them to hide in the laboratory.
The witchers were losing, attacked by both humans and monsters controlled by Kitsu, allowing Tetra to enter the mages' hideout with the intention of killing them. Suddenly, an angry Vesemir burst onto the roof, ready to defend his allies. The elf then tricked him with an illusion, causing Vesemir to accidentally murder Reidrich and his mages.