Full Name: Order of the Solar Temple, International Chivalric Organization of the Solar Tradition
Solar Temple remains the gold standard among apocolyptic space-travelling death cults (how tragic that this should even be a genre). Their membership reached as high as 442 at peak in 1989. The organization was smaller when it reached prominence in 1994 and 1995 through the ritual suicides of 74 members, including its founders.
Frenchman Luc Jouret and his Belgian colleage Joseph Di Mambro founded the Order of the Solar Temple in 1984. Both had prior histories with Templar and Rosicrucian secret societies and fringe religions (and darker things as well -- Jouret had been convicted of fraud and Di Mambro had apparently been a member of the Gestapo). Jouret presented the public face of the new organization, while Di Mambro ran their "back office".
Jouret gave lectures in which he described a global organization; members would join local cells and could later graduate to the International Chivalric Organization of the Solar Tradition itself. He claimed to report to a secret cabal of "Masters" in Zurich, and to have achieved magical powers thanks to the cult's arcane knowledge.
The Order of the Solar Temple was a Neo-Templar organization, and many of its beliefs and rituals are in line with others of that type. Jouret and Di Mambro believed that, because of environment crisis and other problems, the world was in big trouble. The Solar Temple seemed to be looking for a group of people who would be strong enough to survive when society collapsed into anarchy and warfare.
Members of Solar Temple believed that they were "noble travelers" who had been reincarnated on Earth with a specific mission, before returning to their true home.
According to a testament left by a member who skipped the 1994 mass suicude, but offed himself the next year,
"I, a Lightbearer since the most remote times, the time which was given to me on Planet Earth is completed, and I go back freely and willingly to the place from which I came at the beginning of the times! Happiness fills me, because I know that I have fulfilled my duty, and that I can bring back in Peace and Happiness my capitalized energy enriched through the experience which I have lived on this Earth -- back to the Source from which everything comes. It is difficult for the man of the Earth to understand such a choice, such a decision -- to leave willingly one's terrestrial vehicle! But such is it for all those who carry with them Light and Cosmic Consciousness and know where they go back.
"According to the Solar Temple, 26,000 years ago, the Blue Star (related to Sirius's energy) left on the earth 'Sons of the One;' it appears in the sky every time it is needed and responds to magnetization when humanity lives its crises of transmutation"
Things were good for a while but in the early 1990s, some members began distancing themselves from the group, attending fewer events and cutting off donations. Some donors even began asking for reimbursements. Di Mambro's own son, Elie, publicly doubted the existence of the "Masters" and announced that he had discovered that the spiritual phenomena shown onstage at his father's lectures were fake. At least fifteen members, disillusioned, left the Solar Temple.
Di Mambro took this hard, especially the defection of his son. He and Jouret began preparing their group for a "transit" to another world.
On the night of October 4 to October 5, 1994, 53 member of the Solar Temple were murdered or killed themselves in Switzerland and Quebec. In December of 1995, another sixteen followed suit. In March of 1997, five more people died in Quebec, leaving behind three teenagers who refused to participate, but who were able to partially explain how it happened, and to attest to the fact that every member of this final group had voluntarily committed suicide.
Sources:
AFP April 19, 2001
Jennifer Sloan's 1999 overview for the University of Virginia's Soc 257: New Religious Movements class,
http://religiousmovements.lib.virginia.edu/nrms/solartemp.html