Pendule

A legendary wizard from the time of the Order's founding, a master of illusion and a great trickster. In Fifth Edition, he founded the Followers of Pendule Mystery Cult (HoHMC 102), that maintain his Illusion Mysteries.

References

HoHMC 102 provides the description of the Cult and the magus, while hinting he may have initiated other traditions in other Houses.
In Fourth Edition, The Mysteries pages 156-158 links the cult to Orphic and Pythagorian mysteries, and mechanically to totally different Mysteries.
Was Pendule a follower of Plotinus? Timothy Ferguson's Games From Folktales podcast/blog on Pendule.