Mordenkainen

Mordenkainen is one of the most powerful wizards in the history of the multiverse. Everyone has heard stories of him, and in Sigil mothers will use his name to scare children to behave -- "Mordenkainen lives still and he can see anything you can do! Don't make him turn you into a froghemoth!".
The Kateesh have recently learned that Ardent, the adoptive brother of Fiona Hylon, was a cloned body of Mordenkainen. Furthermore, the dead cloned bodies of Mordenkainen are being used by a mysterious shady human who the Kateesh know only as "Ryan". Two different cloned dead bodies of Mordenkainen have been used to open a portal to The Tarterian Depths of Carceri in a swamp near the Olympian Glades of Dionysus in The Olympian Glades of Arborea. This swamp seemed unusual in its placement and in that it contained both a portal to Sigil and to Carceri in very close proximity.
The Kateesh learned that one such cloned body lies ready and waiting for Mordenkainen's soul  in The Sigil Clone Chamber in the Lady's Ward.