Thaddeus Valentine is a handsome hero. He's an intrepid adventurer who has fearlessly explored the globe. He's a "former scavenger who had risen to become London's most famous archeologist" (2.7), who recovered priceless artifacts and is an idol for the citizens of London. Sounds great, right?
It takes about three chapters of Mortal Engines before you realize what a dirty, rotten scoundrel Valentine actually is.
Here are just a few of his offenses: killing Hester's family to retrieve MEDUSA; retrieving MEDUSA, a weapon of mass destruction; pushing Tom to his death; killing Anna Fang. We could go on and on if we weren't running out of space. On top of all this, he's written books about his heroic adventures, no doubt embellishing certain details to convey a specific image.
Valentine's may not be entirely evil. He truly loves his daughter, Katherine. He tells her that he's done all these horrible things so that she might live a comfortable life. Wow, thanks, Dad. The real problem with Valentine is that he's in so deep with Magnus Crome that he can't get out. It's like he's in the mob or something. Someone describes Valentine as a guy "as loyal as a dog, so long as we give him plenty of money and he gets to pretend that foreign daughter of his is a High London lady" (21.18). Sounds like a great guy.
Until Valentine suffers a personal loss—he kills his own daughter by accident—he sees life as a game. "It's the greatest game of all" (28.36). If life is a game, Valentine's the guy hiding the Q tile up his sleeve in Scrabble or printing counterfeit Monopoly money. Life only seems like a game when you're the type of person who will do anything possible to win it.