A'aisa (also Akaisa or Aisa) is the pre-eminent culture hero and trickster-demiurge of the Mekeo and the neighbouring Roro of Papua New Guinea's Central Province, and the central figure of an otherwise sparse mythology. The myth cycle recounts how A'aisa came among an early human community disguised as a filthy, sore-covered old man; mocked and denied hospitality by all but a few, he retaliated by withdrawing the possibility of immortality and releasing death, deadly sorcery and affliction into the world. Before departing westward to the land of the dead he bequeathed to humankind the esa, the body of magical spells and sorcery techniques, together with the charter for the ritual offices that order Mekeo society. Sources differ on his parentage and on the manner of his departure. Michele Stephen's A'aisa's Gifts (1995) treats him as the mythic origin of both sorcery and the 'hidden self', while Mark Mosko's Quadripartite Structures (1985) analyses a bush Mekeo variant in which the hero travels with a companion.