Mossy was a chieftain. He was sacrificed as part of a ritual and buried in the Boglands.
Queen Xenotime managed to reanimate Mossy under the guise of witchcraft as part of her bog warrior army. However, Mossy began to secretly work with a young boy named Root in the hope of overthrowing the Queen and returning Princess Ash to power.
Mossy was eventually stabbed in the heart by his friend, Sphagnum, who was afraid of betraying Xenotime and died again when Ash used her shoes to destroy the bog army. (PROSE: The Bog Warrior)