Aum Shinrikyo, a Japanese doomsday cult started by Shoko Asahara in 1984, carried out one of the deadliest attacks in world history; in 1995, 12 people died and thousands were injured in a terrifying sarin nerve gas attack on Tokyo's subway system. Asahara convinced his nearly 2,000 followers around the world that humanity would end in a "nuclear Armageddon" in 1997 (to be fair, the movie Armageddon did come out the following year) and that in order to survive the "end times," they would need to pledge allegiance to Aum Shinrikyo.
It took eight long years to try Asahara for the subway attack, but in February 2004, he was found guilty on 13 charges and sentenced to death by hanging. He remains on death row to this day. In 2007, the cult split into two breakaway groups, Aleph and Hikari no Wa, and they have been designated as a terrorist organization by several countries, including the United States.