A million years ago, the Progenitors (or the Masters, as they called themselves) built a galactic empire spanning almost all of what is now Lor, Grue, and Khanate space. Using their vast power, the Progenitors seeded themselves across space using wormholes, planting "dragon's teeth" of cuckoo-like offspring on planet after planet, offspring that would one day rise up and transform their homeworld into part of the Masters' kingdom. They saw themselves as protectors and patrons of the Lowly races of the cosmos - but their noblesse oblige came at a cruel price. Worlds that rose up were brutally crushed by the vast physical powers of the Progenitors themselves, then cut off from the wormhole network to deny them the benefits of Galactic civilization. Finally, an alliance of star systems and races now largely forgotten in their own turn rose up against the forces of the Masters and overthrew them via their own vast engines of destruction. Progenitor worlds are these days burnt-out shells or bombed-out ruins, orbiting a mysterious chain of dead stars and supernova remnants scattered through the Galaxy.
Until the Communion came, and visitors to Kesteven 79 awoke the last remaining Progenitor - Lelak, once a clan leader, now the last survivor of a dead world. Lelak fled his planet ahead of the "Isopteran" forces that followed the Praetorians there, watching as the planet was torn apart by the master wormhole opened by the Communion. Watching his planet burn, knowing all he had known, all he had loved, was gone, Lelak vowed revenge - and more. The Isopterans had been annoying parasites in Lelak's time, termites gnawing away at the foundation of the gateway network. The fallen state of the Galaxy had allowed the Isopterans to grow - he would build, from himself, a new galaxy ruled by those who had always ruled it best.
He traveled the Galaxy during the Incursion, tracking down the surviving worlds populated by Master colonists, and finding in those people the ones carrying remnants of Master DNA. Using certain machines, he took those people for his own, amplifying the Master DNA to give them powers and abilities far beyond those of their species while at the same time suppressing the bothersome memories and empathy that might have kept them from their true destiny. Now, from his fortress in orbit of the super-giant NML Cygni, he sends his Children out into the Galaxy to find the lost remnants of the Masters, mighty artifacts that will let them turn back the clock of history and reclaim the galaxy as theirs. It's only a matter of time.
Lelak's Children are like him, fast, strong, and invulnerable, with a fanatical devotion to the cause. They can be found in wretched hives of scum and villainy, hiring middlemen or working themselves to track down lost artifacts to rebuild the power of the Masters. They can be found infiltrating museums and other archeological sites, eager to 'liberate' what is 'theirs' from the Lowlies that dominate space these days. They can be found in almost any species, and are nearly undetectable as such until they use their powers and their skin flushes a familiar shade of dark grey.
With the power of the Bronze Age Superman and the soul of a messianic conqueror, heroes are advised to bring powerful friends, and lots of them, if they choose to fight Lelak. He will choose to do non-lethal damage in the first round or two; he is actually something of a humanist for his people and dislikes carnage. If he is actually injured in a fight, however, or if his Children are killed - all bets are off.