Basileus was an astronomer who lived during the 15th century.

At one point, he was possessed by a demonic entity of some kind, and wrote The Arcanum. Inside, he put explicit instructions on how to build and activate a machine with which to open and control the Ocularis Infernum. According to an early draft of the script for Thirteen Ghosts, when the Church read the Arcanum, they burned Basileus at the stake.