National Geographic: The Final Report: Heaven's Gate

Heaven's Gate was an American UFO religion based in San Diego, California and led by Marshall Applewhite (1932-1997) and Bonnie Nettles (1927-1985). The group's end coincided with the appearance of Comet Hale-Bopp in 1997. Applewhite convinced 38 followers to commit suicide, which he claimed would allow their souls to board a spaceship that they believed was hiding behind the comet.
(Wikipedia: Heaven's Gate)