Hyperion is stopped from reforming in Tartarus by his brother Bob the Titan, his tree having apparently died which sent him back to Tartarus. He and Krios are seen later guarding the Doors of Death. Both are obliterated by the physical form of Tartarus as a show of power. Koios – Lord of the North. In The House of Hades, Koios is briefly seen in Tartarus. He mentions that his daughter Leto had been mistreated by Zeus after "she bore him those fine twins" (a reference to Apollo and Artemis). Percy describes Koios as having Apollo's smile and Artemis's eyes. Krios – The Titan of Stars and constellations and Lord of the South. Percy first sees Krios in a dream during The Last Olympian. He wears armor decorated with glowing stars. In The Lost Hero, Jason claims to have defeated Krios in single combat on Mount Othrys (located on Mount Tamalpais in San Francisco) at the same time of the events happening in The Last Olympian. In The House of Hades Krios is seen with Hyperion guarding the Doors of Death. Both of are obliterated by Tartarus's physical form. Leto - The mother of Apollo and Artemis. In The House of Hades, Koios suggests that she may have been destroyed and sent to Tartarus at some point as he expects her to have finally reformed by now which takes longer for the peaceful Titans. In The Dark Prophecy, Lester has a vision of Leto begging Zeus to lift Apollo's punishment and allow him to return to Mount Olympus. Zeus refuses stating that Apollo's real test is yet to come. Oceanus – The Titan of the Ocean. Oceanus is depicted as having the upper body of a muscular man with a long beard and horns and serpentine lower body. He did not fight the Olympians in the original Titanomachy, but in The Last Olympian, he assaults Poseidon's forces underwater. Oceanus is incredibly powerful and his intense battle with Poseidon lasts for days and creates storms and tsunamis. After the defeat of Kronos, Oceanus escapes back to the depths of the ocean. Prometheus – The Titan of Forethought. Like Oceanus, Prometheus prefers to fight for the more powerful side. He supported the Olympians in the first Titanomachy but joins with Kronos in the second, in part because of Zeus's cruel punishment for Prometheus's gift of fire to mankind. This punishment ended only