Riggath

In one of the outmost layers of hell, there was an accumulation of negative energy that, due to its proximity to the material plane, began corrupting the remains of the creatures that went to die to that place. Over time, and with the revival of the demon Lord, this negative energy gave rise to an abomination made entirely of bones, who later came to be known as Riggath. Having not a soul of his own, Riggath craved the souls of others, needing to consume them to preserve his existence. As time passed, Riggath started to grow more powerful with each soul he consumed, and he became able to use his power to bring more piles of bones to life, slowly building an army of skeletons.