The Hyperions were a race of sentient suns.
The Hyperions were a fusion of DNA, nuclear energy and hyper-intelligence. Their evolution was akin to that of suns. The final stage made them burn up, the energies within them mutating out of control, leaving the entire species on the verge of supernova.
Hyperions used fusion-webs to encircle suns and transfuse their energy into their own bodies, thus prolonging their existence.
Hyperion ships were semi-sentient, designed to evolve and adapt. For instance, Rann-Korr's ship took control of the Dollar Intergalactic terraforming technology on Isen VI. They also employed sensor-shields to avoid detection. (COMIC: Terrorformer)
They also possessed matter manipulation technology. This generated a regeneration field that could reanimate dead bodies into zombie-like creatures called the Scorched. They were typically used as fodder on the planets the Hyperions invaded.
Enslaved worlds were overseen by Fusion Angels. These were essentially reanimated corpses imbued with Hyperion fire. They looked like a human constantly burning, were capable of flight and could shoot deadly blasts of fire. The human consciousness was wiped but it was possible to regain their free will, such as the case of Major Weir.
The Hyperions used Neural-usurpers as mind control technology. It overrode the free will of a victim and would turn them into a mindless drone. They manufactured enough of these devices to enslave whole populations to be used as slave labour to construct the parts of their fusion-webs. (COMIC: The Hyperion Empire)
The Hyperion were a highly advanced species. They left their homeworld on a quest to enlighten the lesser races of the universe, to make it a better place, which earned them the description of a guiding light of the universe.
At the last stage of their evolution, the Hyperions turned from benevolence to malevolence. They began to subjugate various species, including those whose civilisations they had helped create. The Hyperions would encircle the suns with a fusion-web and drain them from their sustenance to prolong their own existence.
The Time Lords, Silurians, Sontarans and other races formed the Alliance of Races to stop the Hyperions, and declared war that came to be known as the Great Inferno. The war wiped out most of the Hyperions.