The Selfish Gene by Richard Dawkins. Blew my mind out the back of my head in high school. Changed the way I looked at the world. Made evolution make some sense, and to some degree, paired with the extended phenotype, helped society make more sense. So much of altruism, racism, and tribalism have roots in game theory of you accept the hypothesis of the gene as the unit of natural selection.

But, perhaps more importantly it taught me by example how to make a good argument that can be rooted in multiple deep disciplines but accessible to the masses.