Octomus the Master

Octomus is the true leader of the forces of darkness and Supreme Master of the Underworld. The denizens of the Underworld revere him so much that they refer to him only as "The Master". He contacts his minions via the white pool at the center of their lair, which turns red to signal his presence. His true form was revealed to be an immense Lovecraftian (Cthulhu) tentacled demon with dragon heads on the end of each tentacle, but usually only his eye can be seen. His other eye is embedded in Koragg's shield, and one of his fangs was used to make Morticon's sword (which was taken by Koragg when Morticon was destroyed and forged into a new Knight Saber) and quite possibly some of his claws were given to Necrolai, her "Claws of the Master".

He was sealed in his Pit by the efforts of Leanbow at the end of the Great War, when the Morlocks attempted to invade the Surface Realm, but he was able to transform his enemy into his servant Koragg the Knight Wolf beforehand. He was also responsible for dragging Catastros down to the Underworld. With the Morlocks active once more, their sole motivation is to free their Master.

Octomus has often had to intervene to stop his minions squabbling - in one case, Koragg was placed on trial before him, accused of being a failure to the Morlock's cause, and he made his verdict in Koragg's favor. He also created Imperious out of the mummified remains of Calindor.

To gain Octomus' favor after his attempts at usurping him had failed, Imperious proposed the idea of feeding the Ranger's Legend powers to Octomus, giving him the power to enter the surface world. But when Udonna's interference almost got her killed by Octomus himself, Koragg stopped him at the last second and was turned into Leanbow once more. Octomus was able to partially emerge onto the surface before Leanbow pulled off the ultimate sacrifice, seemingly destroying himself and Octomus. However, the Ten Terrors are confident that by following the rules of Darkness, Octomus will return.