The Nerb King, as his title suggests, is one of the Nerbs and the rightful ruler of the Nerb Kingdom. However, he disappeared sometime after the formation of the Nerb Dark Egg Legion, and is sought after by the Nerb Freedom Fighters.
The Nerb King and most of his subjects willfully isolated themselves from the rest of Mobius, wanting nothing to do with outsiders. When Dr. Robotnik's machinations threatened his domain, the Nerb King ended up wrongfully accusing the Knothole Freedom Fighters of being responsible. Eventually, however, he was convinced of his error, and hailed the group as heroes. Sadly, many of his people gladly sided with the Eggman Empire, and the king himself disappeared. His daughter, however, became a member of the Nerb Freedom Fighters, who continued to search for him even as they fought against the Nerb Dark Egg Legion. (StH: #10, CSE)