I was inspired by the Biblical story of the Madness of Nebuchadnezzar, in particular this rather famous painting by Robert Blake.
The anatomy of the creature was based on a Northern Pike — also known as a Jackfish — a fearsome carnivorous fish that lurks in the lakes and rivers of the Northwest Territories.
I thought: what if somehow Samatar merged with a jackfish … almost as if the fish had died while consuming him, leaving them as a zombified hybrid creature cursed to haunt the underworld forever.