In the legend, The Monster-Slayer duels with rival Sith, The Dreamer. The duel ends with both dead, the two Sith overwhelmed by the vapors of the .
According to Luke Skywalker, the legend was rooted in fact, and took place circa 3400 BBY.
At some point, Skywalker acquired a depiction of The Monster-Slayer's duel against The Dreamer, which he annotated sometime after the Emperor's death in 11 ABY along with a copy of The Jedi Path and Book of Sith.