This article traces the history of Mumboism, a millennial cult of south-west Kenya, 1912–34. Mumbo, the serpent god of Lake Victoria, promised to eject whites and chiefs from the region and usher in a period of prosperity. Mumboism gained followers, it is argued, because it mixed older ideas of patron–client relations with newer ideas of omnipotent, unseen beings, introduced by Europeans as Government and God. Mumbo challenged chiefs and missionaries, struggling to create patronage networks, by attracting clients, and threatened to unmask Government and God as impotent. Chiefs and, to a lesser extent, missionaries directed state power to the repression of Mumbo, eliminating it before it could undermine the very basis of European power.