Illuminati - How It Began .....

To my knowledge, the term "Illuminati" has been used by various groups such as the "Illuminated Ones" in the 11th century. A 15th century German "Illuminati" group claimed to have received illumination from Satan, believed to be the angel from heaven, Lucifer, said to be the bearer of light

There was another group in Afghanistan during the 16th century in search of illumination from the Supreme Being and in need of a class of perfect human beings. Upon attaining the 4th degree level, members would become the "Enlighten One" and would receive mystical abilities. When they attained the 8th degree level, they were told to have become perfect. All this was to foster influence among the elite for peace on Earth. At the same time they were warring the Mongols who were the power in India. This group existed until the 17th century. After that other groups or brotherhood began to mushroom.

I guess when Adam Weishaupt studied the writings on the brotherhoods and their practices, he had already adopted their doctrines and practices in his own brotherhood to stand up against religious suppression and also to change their religion to a religion "of reason".