Humans define themselves through personhood as agents in society. To become persons, children differentiate their self from others. They take, as George Mead (1934) says, the other and self-objectify by predicating a sign-image or trope upon themselves. Birth rituals realize these tropes with the child's body as tool and raw material. Birth almanacs in Highland Mexican codices depict, as I argue, the transformation of a child into a person. Patron gods pierce the child, display it, manipulate its umbilical cord and nurse it. Gods provide the child with vital life forces while the child and future adult nourishes the gods through sacrifice. The birth almanacs situate Aztec personhood in a covenant of humans with gods. As children mature, bodily changes metonymically express the metaphoric relationship of the children with their patron gods. In the bathing ceremony, fellow humans — especially the child's parents and the midwife — step into the roles of the patron gods and perform the above activities on the child. Aztec children other themselves in gods through ritual practices. By connecting the ideology and practice of personhood, the birth almanacs are a theory of social action.