Zavist was a mage from Kovir. He and Stregobor were advisors to Idi, King of Kovir. Based on their advice, Idi banished Geralt rather than paying him for the amphisboena he'd slain.
||'Our last meeting,' said Geralt, 'was in the court of King Idi of Kovir. I'd come to be paid for an amphisboena which had been terrorising the neighbourhood. You and your compatriot Zavist vied with each other to call me a charlatan, a thoughtless murdering machine and a scavenger. Consequesntly not only did Idi not pay me a penny, he gave me twelve hours to leave Kovir and, since his hourglass was broken, I barely made it.
He is mentioned in the short story "The Lesser Evil" which is included in The Last Wish collection.