The term "Illuminati" refers to the Bavarian Illuminati, a secret society that operated for only a decade, from 1776 to 1785. This organization was founded by Adam Weishaupt, a German law professor who believed strongly in Enlightenment ideals, and his lluminatenorden sought to promote those ideals among elites. Weishaupt wanted to educate Illuminati members in reason, philanthropy, and other secular values so that they could influence political decisions when they came to power.

"It was pretty ambitious for six or nine guys, but they really wanted to take over the world," says Chris Hodapp, the co-author of Conspiracy Theories and Secret Societies for Dummies with Alice VonKannon.

The Illuminati's goals — and reputation — often exceeded their means, Hodapp notes. In its early days, the group was just a handful of people. And even at its largest, it only consisted of somewhere between 650 and 2,500 members. The group grew to that size by becoming a sort of sleeper cell within other groups — Illuminati members joined Freemason lodges to recruit members for their own competing secret society.