METALKIND

Planet of Origin: Metalking planet, part of a binary planetary system (the other planet being the Fleshkind planet) in the eye of the Tornado Nebula.

The Metalkind is a species of sentient  humanoid bio-metalloid  boron-based lifeforms. The Metalkind was at war with a Fleshkind race that lived on the twin planet of their homeworld after they started mining operations to mine precious ore on  the Metalkind planet; ore which was in fact the the Metalkind's children - which were then used as slaves by the Flehskind, leading to the war.

This leads to believe that the Fleshkind was originally more technologically advanced than the Metalkind, being the first one to venture on the other's planet and starting its exploitation. As of the 21st century, after hubndreds of years of war, both species possessed weapons that enabled some kind of stalemate bwetween them, as well as interstellar-range teleportation technology - which might have been the initial way the Fleshkind made it to the Matlakind planet.

To end the stalemate, the Fleshkind had developed a  living weapon that could destroy the Metalkind but the weapon was lost, possibly restoring the stalemate.

Source: Doctor Who Universe, (SJA: Sky)