The Minotaurs are a minotaur-like humanoid species that developed a parasitic spacefaring civilisation on an interstellar scale. Parasitic by nature, they fed on the faith of other life forms and survived by descending on primitive planets, setting themselves up as gods to feed on the worship of the natives. They could not feed on a person who held no strong beliefs. After a while when species became advanced, they usually managed to expell them upon realising their true nature.
A more dangerous offshoot of the species, called Nimon, could effectively drain not only faith but the very life force of their victim and could shoot blasts of energy from their horns. The Nimons were able to consume to extinction the population of an entire world within a few years. As their food source got scarce, they would look for another planet ripe for conquest and draining. A scout would descend on a planet, representing itself as a god with gifts of advanced technology and start to construct a maze-like Power Complex designed to generate a portal back to the Nimons' current planet. The Nimons would then migrate en masse to the new planet using capsules sent through the portal, drain that world dry and look for the next, continuing the cycle they referred to as the Great Journey of Life.
They are said to have been one of many races that participated in the Millennial War some 150 million years ago against the Mad Mind of Bophemeral where they collaborated with the Osirians in dropping quantum collapsers on the insane computer intelligence. (PDA: The Quantum Archangel). At some point after the third millenium, after having drained the planet Crinoth, all traces of them was lost while they were travelling via their their portal toward their next prey, the planet Skonnos.
Source: Doctor Who universe, (DW: The Horns of Nimon) (DW: The God Complex)