The ancestor of Gamzee Makara and a member of the subjugglators, presumably the leader. After his kismesissitude for Mindfang failed, Dualscar offered her location to him. Mindfang writes in her journal that this plan either will or already has failed spectacularly due to the subjugglator's sanguinary nature, resulting in Dualscar's death.
He decorated his walls with the blood of his victims. The gory rainbow includes blood of all castes (excluding tyrian purple and his own), which surely pleases him