Dualism in cosmology or dualistic cosmology is the moral or spiritual belief that two fundamental concepts exist, which often oppose each other. Many myths and creation motifs with dualistic cosmologies have been described in ethnographic and anthropological literature. The motifs conceive the world as being created, organized, or influenced by two demiurges, culture heroes, or other mythological beings, who compete with each other or have a complementary function in creating, arranging or influencing the world. There is a huge diversity of such cosmologies. In some cases, such as among the Chukchi, the beings collaborate rather than compete, and they contribute to the creation in a coequal way.
Excerpt from "Dualism in cosmology" on Wikipedia