Alzur was a famous mage and the inventor of many spells, including Alzur's Double Cross, Alzur's Shield and Alzur's Thunder. He is also known for having created many horrible monsters, some of which still roam the world. He is said to have had a voice and diction which were positively mellifluous.
Alzur's teacher was Cosimo Malaspina, while Idarran of Ulivo was an apprentice of Alzur. According to Ortolan, Malaspina and Alzur were the creators of witchers.
His spells were also used by other mages. Notably, Fregenal may possibly have used the spell known as Alzur's Double Cross to create Koshchey.
During his visit in the Outskirts of Vizima, the witch Abigail tells Geralt about the time Alzur the mage met a beast immune to magic. The beast asked the mage a question, and by answering correctly Alzur was able to defeat it. Thenceforth, the beast was known as "Alzur's demon".
Berengar's notes on the Beast confirm that the Beast haunting the Outskirts could be "Alzur's demon".
Over the course of the game, Geralt also comes upon a book called The Double Cross of Alzur, which is an edited and censored edition of Alzur's original work which revealed how to create a koshchey.
Alzur is mentioned in the Laboratory notebook by Ireneus var Steingard, who cruelly experimented on the witcher Kiyan and compared himself to creators of the witchers.