Heaven's Gate, a religious group, developed a unique theology that blended elements of Christian millenarianism, New Age beliefs, and ufology, leading to its characterization as a UFO religion. The central belief of the group revolved around the idea that followers could attain immortality as extraterrestrial beings by renouncing their human nature. They aimed to ascend to a celestial realm referred to as the "Next Level" or "The Evolutionary Level Above Human." The death of one of the group's founders, Bonnie Nettles, in 1985, challenged their initial belief that they would achieve this ascension while alive on a UFO. They later came to see the body as a mere "container" for the soul, with the expectation that their consciousness would be transferred to new "Next Level bodies" after their physical death.

The tragic culmination of Heaven's Gate occurred on March 26, 1997, when San Diego County Sheriff's deputies discovered the lifeless bodies of all 39 active members, including their leader Marshall Applewhite, in a house in Rancho Santa Fe. This mass suicide was meticulously coordinated to coincide with the closest approach of Comet Hale–Bopp. Just before the event, the group updated its website with a message declaring that the comet's appearance marked the culmination of their "graduation" from the Human Evolutionary Level after 22 years of earthly existence. The name "Heaven's Gate" was adopted only in the final years of the group's existence; it had previously been known as Human Individual Metamorphosis and Total Overcomers Anonymous.