Petrac is a Magyaran pirate who appears briefly in The Invaders.
At Limmat, he is helping Zavac and is in charge of a relatively small group of men at the beach, his job being to defend the palisade. Unfortunately, he is up against the Herons and the Mangler and doesn't stand much of a chance. He calls for reinforcements from Zavac. Zavac says he'll send twenty archers, but Zavac doesn't keep his word and instead makes a run for the The Raven.
Once the Herons land on the beach, he leads his remaining men down to meet them. Petrac ends up fighting against Thorn and being seriously outclassed is killed.