Thaddeus Valentine is a fictional character from the Mortal Engines series, written by Philip Reeve. He serves as a prominent antagonist in the story, known for his ambition and cunning nature. Thaddeus is a member of the London guild and is deeply involved in the politics of the mobile cities, where he seeks power and control. Valentine is also the father of Hester Shaw, one of the main protagonists. His actions and decisions significantly impact the plot, as he pursues dangerous technologies and schemes that threaten the balance of power in the world. His character embodies themes of ambition and moral ambiguity.