From the journal of Jedi Master Arlo Grennen during his investigation into the dark side's influence on Yavin 4:
“Information on Yavin 4 has not been easy to come by, but I have scoured the libraries of Tython and what I have discovered is fascinating.
“The first corruption of Yavin's fourth moon by the dark side that we know of corresponds with the arrival of Dark Lord Naga Sadow some fourteen hundred years ago. I'm not entirely sure whether Sadow was drawn here by the dark side or if he himself planted the first seed of its presence. That's one of the many things I hope to learn while I'm here.
“Sadow was a gifted alchemist who turned his Massassi followers into powerful, violent animals who worshipped and served Sadow. The Massassi built massive temples for Sadow where they sacrificed their own in his honor. Sadow was even powerful enough to stave off the inevitable. He placed himself in a near-death slumber, which he remained in for hundreds of years, waiting until someone would come to take his place….”