I knew the Jedi of the Old Republic, witnessed how the corruption of their philosophy brought the galaxy to the brink of annihilation. By understanding our mortal enemy we will possess the ability to eradicate them.Darth Senex
Darth Senex, born Kelo Fero, was a Force-sensitive Pau'an male who rose to prominence as a Sith in the Dark Lords of the Sith. One of many exiles following the destruction of Byss at the hands of Emperor Validus, Senex was shepherded into the Unknown Regions by his master, Darth Judex, on a three decade journey to search for the Source of the Dark Side.
Homecoming (220-250 ABY)
In the intervening years following the destruction of Byss at the hands of Emperor Validus (known colloquially as "The Dark Ages"), as the Empire split apart and Sith fled into self-imposed exile or sought to establish their own petty kingdoms, Darth Judex stole away his apprentice into the Unknown Regions on a journey to uncover the Source of the Dark Side. Judex was certain that if he could find the Source, it stood to reason he could command the Dark Side in total. In effect, Judex believed he would become the Dark Side incarnate. But as is the case with so many similar quests for power, the trail of clues was at once cold and inextinguishable. Judex, with apprentice in tow, chased each and every thread of information which might bring him closer to his quarry.
The Empire failed us, my apprentice. Our path is now into the unknown, to seek the power which has eluded the Sith from the very beginning.Darth Judex to Senex
As their journey brought them deeper into the Unknown Regions, Senex's training took a backseat to Judex's single-minded determination. This seeded a deep resentment in the apprentice, which grew as they traveled an endless parade of worlds. But Senex had long envisioned himself as the future of the Sith Order, so with his master's attention elsewhere, he continued his own training by utilizing a collection of scrolls and holocrons that Judex had pillaged prior to fleeing the Deep Core.
Late in their travels, Judex and Senex encountered a man claiming to be from the Sith Order on Byss. While news had sometimes filtered in on piggybacked communications from the galaxy proper, the pair had operated under the assumption that the Empire had collapsed and that the Sith were nothing but a memory. Confronted with the possibility that Validus' empire not only survived the destruction of the capital but was indeed flourishing under a new ruler, doubt crept into corners of Senex's heart. Had the limitations of Judex's mentorship reached their limit? Might the bond between master and apprentice have run its course? Was there another way forward that would allow Senex to reach his full potential?
At Judex's insistence, master and apprentice parted with the mysterious stranger to continue their search. But it was not long before the doubts planted during their brief meeting began to bear fruit. Questions which at first sprang from curiosity became chisels expertly cracking away at Judex's patience. For his part, Judex descended into obsessive madness, his every waking moment devoted to the pursuit of the Source. But the closer he believed himself to be, the longer the trail seemed to grow. It did not help that Senex had taken to sabotaging some of his master's findings. He would alter texts or misrepresent interviews with travelers when he reported back to Judex, anything to keep the old man chasing his tail.
After years of languishing under a master who could no longer train his apprentice, Senex's resentment had grown past the point of return. He killed Judex at the point of his lightsaber, deep within a cavern Judex believed contained a map which would lead him, finally, to the Source. In a poetic twist of irony, Senex had discovered the map first and as he waited for his master to arrive, he defaced the stone carving so that it resembled a path which would take them back to Byss.