Unidentified Sith Lord (Athiss)

A Sith Lord ruled on the Outer Rim planet Athiss more than a millennia before the Battle of Yavin, but was betrayed by his allies, killed, and entombed in his temple. Over the years, knowledge of his tomb was lost and became corrupted, leading a group of lore-seekers to believe that it was actually a Jedi tomb and source of knowledge. They journeyed to Athiss, and battled a dark side illusion which took the Sith Lord's image.

Behind the scenes
The Sith Lord appears in the Lost Knowledge adventure in Fantasy Flight Games' 2014 Star Wars: Force and Destiny Beginner Game book.