The Werewolf Principle by Clifford D. Simak

In this science fiction novel, a man named Andrew Blake returns to Earth after being lost in space for over two centuries, only to discover that he has been genetically altered to host multiple personalities, including a werewolf and an alien entity. As Blake struggles to understand his new identity and the powers that come with it, he becomes embroiled in a conflict between the remnants of humanity and the advanced beings that now inhabit the galaxy. The story explores themes of identity, transformation, and the nature of humanity as Blake seeks to reconcile his fragmented self and find his place in a vastly changed universe.