This is an unknown guy, but he is a god. No one has really seen him, but everyone knows who he is. They all know what he looks like too. If people pray and sell their soul to him, he gives them powers. However, the twist! He only gives it to evil beings. The 2 main to sell their souls were Rodrick and Error Weegee. He has fun torturing people. He enjoyed to see Wario panic for help, and he even laughed about it. Only Roxx and Wario have seen and met him in real life.
I DON'T CARE
He made a room for Rodrick, and tested him. The problem with it, was if Rodrick failed, he'd be forever stuck there. When Rodrick managed to escape the room, he was to drop a key into a Warp Pipe. The key fell into the Basement. The point was so make Branch freak out some more, while Illuminati watches.
Luigi and Mario have both challenged him the first ever in the franchise to a battle. Mario lost, but Luigi won in a tie. He has interesting powers one being to clone. Mario lost because 2 clones crushed him from end to end, and he was electrocuted. Luigi managed to socket one of the clones each time and throw punches into his eye.
The New Plan
After his research of watching over existence, he discovered AGK. This was from the help of watching Icecream Man. He told everything to Roxx. He also said AGK was friends with Mario, and this seemed to make Roxx wanna destroy AGK. Plenty of times in the past as well, his team has went after AGK, but for the most part at the time, Roxx didn't know AGK.
It seems Illuminati has family issues. He has a daughter named Erica, and an ex wife he had divorced. He can rarely see her daughter. He decided to send Roxx to kidnap her. Afterwards, Illuminati wanted to make her daughter just like him. Erica was sent to go to Earth and cause chaos and destroy it.