Bjorg was a master shipwright in Kaer Trolde Harbor during 1272 and where he was training his apprentice, Rurik. Finally fed up with what he perceived were just drowners killing people near the cliffs, he decided to find someone to take care of the problem.
If Geralt accepts the contract: He informed Geralt the two known witnesses he remembered seeing the monster's attack: his apprentice, Rurik, and a widow named Tove.