What was Heaven's Gate, and why did its members believe in a Next Level?

Heaven's Gate was an American new religious movement, founded in 1974 and led by Marshall Applewhite and Bonnie Nettles, who were known to members as Do and Ti. It is primarily known for the mass suicide of its members in 1997. Its central belief was that followers could transform themselves into immortal extraterrestrial beings by rejecting their human nature, and ascend to heaven, which the group called the "Next Level".

Scholars have described its theology as a mixture of Christian millenarianism, New Age ideas and ufology, and they disagree over whether it was fundamentally New Age or Christian. Applewhite and Nettles identified themselves as the two witnesses of the Book of Revelation. They published advertisements for meetings, and about 20 people sold their worldly possessions, said goodbye to loved ones and joined in 1975. In April 1976 the group stopped recruiting and became reclusive, with a rigid set of behavioral guidelines.

On 26 March 1997 the bodies of the 39 active members were found in a house in Rancho Santa Fe, California; they had taken part in a coordinated series of ritual suicides that coincided with the closest approach of Comet Hale–Bopp. Most people described it as a mass suicide, though sociologist and former cult member Janja Lalich called it murder.