A UFO religion is any religion in which the existence of extraterrestrial (ET) entities operating unidentified flying objects (UFOs) are an element of belief. Typically, adherents of such religions believe the ETs to be interested in the welfare of humanity which either already is, or eventually will become, part of a preexisting ET civilization. Others may incorporate ETs into a more supernatural worldview in which the UFO occupants are more akin to angels than physical aliens; this distinction may be a little blurred within the overall subculture. These religions have their roots in the tropes of early science fiction (especially space opera) and weird fiction writings, in ufology, and in the subculture of UFO sightings and alien abduction stories. Scientology is the largest UFO religion in the world, followed by Raëlism.