Illuminati or the enlightened offshoot 'secret' society of the 'freethinkers' created in 1776 I believe. Disbanded several years later, reasons I cannot recall. I''m sure you can find the actual history about them on Google.
Like the Freemasons and other 'secret' societies they are used all the time for conspiracy theories. Linking hearsay and sometimes completely false 'evidence' for some sort of New world order crap.
No relation to free masons, the American revolution or the French revolution for that matter.