Most Stygian wraiths know Gorool as the Godzilla-like Malfean that threatened the city of Stygia in the closing days of the Fifth Great Maelstrom. Charon in his last act in the Underworld, challenged Gorool in the Weeping Bay and fought him to a standstill before both disappeared in a whirlpool.
What Sister Acceptance and some other senior Pardoners know is that by the early twentieth century, Charon's Shadow was running amok. Even in the periods when Charon was free of Catharsis, he was inevitably going mad. In order to prevent further damage to his sanity and Stygia, Charon submitted himself to a powerful and experimental Castigation. The end result was that his Shadow fled his Corpus and took on a form of its own, somewhat like the Ritual of Severance. The resulting creature called itself Gorool, and reappeared soon after.