"Supergods: What Masked Vigilantes, Miraculous Mutants, and a Sun God from Smallville Can Teach Us About Being Human" by Grant Morrison.
Morrison draws on art, science, mythology, and his own astonishing journeys through this shadow universe to provide the first true history of the superhero - why they matter, why they will always be with us, and what they tell us about who we are... and what we may yet become.