Kratz is one of the sergeants from Castle Wittgenstein. You meet him when he impounds your boat at Wittgendorf on Aubentag 6th Vorgeheim. The next day, Marktag 7th Vorgeheim, whilst you are in the forest heading for the tunnel under the outer bailey, you encounter Kratz on horseback, leading a patrol.
You attacked the patrol along with Hilda Eysenck, your guide, but you found Kratz to be a dangerous opponent who very nearly killed Thrumir Bhakdram with a blow from his flail.
Kratz was fatally wounded by Fleck and finished off by Ravenclaw Darkwood as he lay bleeding to death on the ground.