This lore can be found on Dromund Kaas.
The Sith Lord Parnax vanished forty years ago, leaving no one to mourn his passing. Deeply unpopular even among his own family, Parnax spent his brief career betraying every ally while acquiring an impressive list of highly placed enemies. Whether consumed by arrogance or simply too stupid to predict his eventual fate, he appears to have deliberately invaded the Dark Temple long before the most recent incursion, seeking the key to the Emperor’s power. According to the last few entries of his journals, Parnax found himself unable to leave the Dark Temple after entering it, becoming lost and disoriented. His recordings descend into mad, incoherent ramblings about an all-consuming darkness extinguishing all life in the galaxy. Convinced he could survive this coming doom by merging with the Force, Parnax illogically schemed to end his own life.