Though Kami Garcia’s new novel Unbreakable features a fictional secret society called the Legion, a lot of the story is inspired by real-life research. One of those things is the Illuminati.
If you’ve read Dan Brown’s Angels & Demons you may have heard of this group before, a real-life secret society dating back to the 1700s. Granted, much of what we do know about the Illuminati is questionable — and the group has become the source of many conspiracy theories. According to Wikipedia:
Historically the name refers to the Bavarian Illuminati, an Enlightenment-era secret society founded on May 1, 1776 to oppose superstition, prejudice, religious influence over public life, abuses of state power, and to support women’s education and gender equality. The Illuminati were outlawed along with other secret societies by the Bavarian government leadership with the encouragement of the Roman Catholic Church, and permanently disbanded in 1785. In the several years following, the group was vilified by conservative and religious critics who claimed they had regrouped and were responsible for the French Revolution.
In subsequent use, “Illuminati” refers to various organizations claiming or purported to have unsubstantiated links to the original Bavarian Illuminati or similar secret societies …
You can read more scholarly information about the Illuminati here.