He is one of Yennefer's long-time lovers whom she had known for many years, often visiting and staying with him for several months. During one such occasion during with Geralt had travelled to Aedd Gynvael with Yennefer the two men learned of each other. Both Istredd and Geralt are unwilling to share Yennefer, with Istredd not caring if Yennefer has several non-serious lovers, but refuses to share her with someone she is seriously involved with. During this time when Yennefer was with him he asked her to marry him and live together with him at his residence. Yennefer does not immediately give him an answer and becomes torn between picking Istredd or Geralt.
Istredd and Geralt then challenged each other to a duel to the death for the right to exclusive access to Yennefer's affections (although they both knew whoever won would have to hide from her for some time until her rage ended). Both believed that Yennefer could not decide between them, however before going to fight Geralt, Istredd received a letter from an enchanted Kestrel sent by Yennefer telling him she has chosen to leave him. Istredd in grief over this turned up to the fight bearing a sword instead of magic hoping that Geralt would then kill him.
Geralt having contemplated suicide himself that night, went in an alley without weapons to be killed by thugs, but they fled once they saw his eyes. Geralt met him in the agreed location, but once Geralt found out that Yennefer had left Istredd the same letter he know's is waiting for him, he decided to leave, and read his letter, and left without fighting.
Istredd proposed to Yennefer while she was with Geralt in Aedd Gynvael. He promised her stability, a home, a future, and the child(ren) she's longed for. However, Yennefer left the city even before Geralt, and Istredd ended up helping Geralt when he faced Dermot Marranga and his men.
Played by Bronisław Wrocławski.