Promethean

Superficially, the Prometheans were a very elegant race, possessing smooth gold skin and long-limbed bodies, identifying themselves as teachers and shapers out to aid the progress of lesser races, claiming to have done so since the dawn of conscious thought. However, their appearance concealed a cold heart, disdaining emotions among 'lower' races - dismissing The Doctor as arrogant and undisciplined -, claiming that they were doing humanity a favor by stripping them of their higher emotions, when their true objective was simply to reduce human mental development to a point where they could do nothing but worship the Prometheans, regarding their actions as eliminating the higher concepts that troubled humanity so that they would no longer be troubled by disease, injury, or environmental changes.

The Prometheans were attracted to Earth when the First Doctor materialized in the distant past just as they were passing by, the chronal ripples created by the TARDIS's materialisation drawing them to Earth in time to witness how the First Doctor, Susan, Ian Chesterton and Barbara Wright - particularly Ian and Barbara - taught the primitive Tribe of Gum how to make fire, unite against others in defense, and the strategic benefits of subterfuge. Feeling that the TARDIS crew's work to inspire the Tribe of Gum to develop should continue after their abrupt departure, the Prometheans supplied the Tribe with various samples of psychic metal, which the Tribe shaped into weapons as they became leaders of the other Tribes. However, when their immediate supply of psychic metal was exhausted as the Tribe grew too large, the Tribe of Gum were sent out to find more metal, equipped with armour that would slow their aging and allow them to withstand even faster-than-light speed without any trouble, but also asked that the Prometheans provide them with 'Teacher' and 'Woman' - Ian Chesterton and Barbara Wright - so that the Tribe could learn more from them.

Over the centuries, as the Tribe of Gum searched space for more psychic metal - their efforts warping space so that they only aged a few years as they travelled despite the subsequent centuries -, various other samples of psychic metal were found on Earth as humanity developed. These samples included an old woman in ancient Greece using a 'Belief Engine' powered by a piece of the metal to create the gods of Olympus, an alien artist imprinting his name on the entire population of London - turning everyone in the city into a silhouette figure with his name 'written' on them -, or a sixteenth-century Czech rabbi transferring his mind into a golem powered by an orb of psychic metal. Although the Eleventh Doctor, Amy Pond and Rory Williams were able to resolve these problems, The Doctor was left concerned about both the origin of the psychic metal and a mysterious message that those who used the metal asked him in the aftermath; 'What lies buried in man?'