Elder Races is a catchall term for the first generation of space-faring species to arise in the galaxy. At least one of them was responsible for building the first Altspace Portal and NavCom beacon network, as every known species learned Altspace travel either from an older species or from reverse-engineering an ancient Altspace Portal found in their own system.
Aside from a handful of ancient portals and beacons, no other evidence of their existence has ever been found. Stories of them are as much myth as educated guess. They are assumed to have been tremendously advanced, some theories even attribute the rise of later generations of intelligent life to them as a form of engineered "uplift", one proposed solution to the Humanoid Paradox.
Though all evidence suggests they are long extinct, some believe they are in hiding or have left to explore beyond the Milky Way Galaxy. Some people also claim that they actively manipulate galactic civilization to maintain a uniform level of technology in space-faring races. Some conspiracy theories claim that they periodically wipe out civilizations that become too advanced so no one can ever catch up with the Elder Races as a threat, or that they are performing some kind of extended anthropological experiment and keep starting over periodically.
Some legends claim they are destroyers rather than creators, as all known space-faring species currently in existence developed interstellar travel within the last thousand years or less. Every older civilization went extinct tens of thousands of years ago or more. Some theorize if the Elder Races ever returned, it would herald a galaxy-wide apocalypse.