Katashka, the Gatekeeper, is one of the Overlords who ruled over all of Eberron during the Age of Demons. Katashka was bound by the dragons and couatl after they jointly discovered the Draconic Prophecy, and the couatl sacrificed themselves to form the Silver Flame.
All of the Overlords embody mortal fears. Katashka embodies our fear of death, and holds absolute mastery over the domains of life, death, and the eternal limbo that is undeath. Katashka was open to making deals with mortals during the Age of Demons, and it is possible that these deals with dragons inspired stories of The Keeper, who is sometimes depicted as a skeletal dragon. Much like stories of The Keeper, Katashka was known for intercepting souls on their way to Dolurrh and twisting them into undead monsters.
The forces of the dragons clashed with Katashka in the Light of Siberys region of Argonnessen, the site of which would come to be known as the Harvest of Pain amongst the dragons.