Augustus is a big name. It’s the name of the first emperor of the Roman Empire, a name one associates with confidence and bravado and marble statues and stuff. Gus is a much shorter, smaller name—the kind of name that appears in children’s picture books, for instance. In some ways, they’re opposites: the one a big, strong man; the other, a fragile and endangered little boy.
Hazel calls him Gus more as she knows him better, as the manic pixie dream boy falls away and she comes to know and grapple with and love this fragile, desperate, beautiful boy.