Brehen

Brehen, also known as "Cat of Iello", is a witcher of the Cat School. He is unbalanced, and probably a psychopath, banned from entering the Kaer Morhen.

In Season of Storms
He had terrorized the inn to force Geralt to duel with him, but finally he let the hostages out. He complained about banishment and thought (wrongfully) that Vesemir had condemned him to death. After perturbations he goes to Vizima in order to collect the bounty for the striga terrorizing city.

In The Witcher short story
He was probably one of witchers mentioned by Velerad during his first conversation with Geralt.

Brehen Brehen Brehen