In private life, however, tradition required that some human beings be treated as more or less divine; cult was due from familial inferiors to their superiors. Every head of household embodied the "genius" – the generative principle and guardian spirit – of his ancestors, which others might worship and by which his family and slaves took oaths; his wife had a juno. A client could call his patron "Jupiter on earth". The dead, collectively and individually, were gods of the underworld or afterlife ("dii manes"). A letter has survived from Cornelia, the mother of the Gracchi, expecting that when she was dead, her sons would venerate her as "deus parens", a parental (or a nurturing) divinity; such piety was expected from any dutiful son.