Soulgutter is a monster created by Saruin to spread havoc. It blended in with the populace and ate souls. Death was infuriated that the cycle of reincarnation is disrupted, so he taught the people how to stop Soulgutter. He could only be sealed since Soulgutter has no soul. To do so they had to build an altar on the Steppes of Galessa and performed a rite to seal it. In the game, Beastmen under the control of Saruin weakened the seal and soulgutter ate the souls of all who came near the altar.
In Uso, around the time Soulgutter is about to be released, Death gives the player a blessing to prevent their own souls from being eaten by it (Negates Soulgutter's ability to deal Life Point damage directly) When the player arrives Soulgutter just emerges from the seal after eating the souls of the beastmen who undid the seal and the player has to circle it 5 times counterclockwise using the PS2's right analog stick after stunning it, or deal 30,000 damage and it will just seal itself again. Soulgutter can also be found in Purgatory.