First Appearance: (mentioned) "The Edge" (appeared) "Vows"
Other Appearances: "Revelations," "To Serve Mankind"
The Illuminati Society is an ancient and secret organization whose exact origins are shrouded in mystery. It was apparently founded by Mr. Duval some time after the fall of Camelot. His purpose in doing so is unknown, but the Illuminati managed to gain their place as the secret rulers of the world relatively quickly.
In AD 975, the Norman Ambassador, an Illuminatus, was given two packages by the time-travelling David Xanatos. One package, containing a 10th-century coin, was sent to 20-year-old David Xanatos in 1975, where it was now worth $20,000. This began Xanatos's own fortune. Presumably, some time after this (or perhaps even during this), Xanatos was inducted into the Society, albeit as a lower-echelon member. The second contained detailed instructions on how to set up his fortune, and arrived in 1995 in time to set up those events.
FBI Agent Matt Bluestone became obsessed with the Illuminati, and sought to prove their existence. To prevent that, his partner, Illuminatus Martin Hacker, threw him on leads that really led nowhere, and the Society set up other 'roadblocks' in his path. Even when he lost his job with the Bureau, and joined the 23rd Precinct of the NYPD, he continued to pursue the Illuminati. In 1995, Matt managed to track down Mace Malone, a former gangster from the 1920s and another Illuminatus. Malone, citing the fact that the Society found Bluestone's searches impressive, offered to make him a member. Malone gave Matt information on Elisa Maza and the Manhattan clan. In exchange, Matt was to bring a gargoyle to the Hotel Cabal, a building filled with mind-damaging traps and tricks, for interrogation. Matt did so, but let the gargoyle he brought- Goliath- in on the plan. Together, they defeated Malone and escaped. Despite that, the Illuminati still allowed him to join, whereupon he learned Hacker was a member.
The Illuminati Society, for mysterious reasons, helped found the Quarrymen. Mr. Duval called Xanatos a few nights after the incident on the Hunter's Moon, but the industrialist pointedly ignored the call to be with his son.
In the Goliath Chronicles, Illuminati scientist Dr. Nexus captured Goliath and the Trio. He used mental torture and hypnotic technology to make Goliath into a living weapon aimed at destroying Latvonian President Egon Pax. Pax's peace-making efforts threatened their sales of arms to both sides in a war his country was involved in. This plan was foiled by Xanatos, the Trio, and Pax himself, but damage was still done- human-gargoyle relations were all but shattered.
In Greg Weisman's Master Plan, the Illuminati would have gone on to be antagonists in "Pendragon" due to their leader Duval being Percival, and in "Bad Guys", the Director would have formed the Redemption Squad for the purpose of defeating the Society. The Society would still exist in 2198, and would have sold Earth out to the Space-Spawn, working against Samson's Resistance.