Shilluk religious concepts are drawn into relief by an emphasis on the creator-god or divinity known as Juok (a common Nilotic term for a spiritual power), the veneration of Nyikang through the persons who become kings, and the recognition of the ways in which the spirits of the deceased can affect those who survive them. Juok is a ubiquitous spirit, a phenomenon manifest in all places and at all times. Juok can be addressed through sacrifice of cattle, goats, and sheep. Juok is also strongly associated in Shilluk thought with the river spirit that first gave birth to Nyikang. Most Western depictions of Shilluk religion have been colored by nineteenth-century visions of "primitive religion." The Shilluk figured prominently in evolutionary schemes put forward to depict the course of religious evolution. Ironically, although the Shilluk have become well known in the anthropological literature, no prolonged research has been carried out by a trained observer in their settlements. Thus, much of what has been written about the Shilluk relies upon data that were collected in an inconsistent manner in the early twentieth century.