This Jedi Insider Custom was done by TheUnknown who has created custom Expanded Universe character who goes by the name the Dark Assassin, Wraith. The Unknown gives some background on this character below:

" A secret apprentice trained by Darth Vader in plans to overthrow Sidious. He posses no Force traits, but is an exceptional swords man. Vader began to train him in the arts of a saber. After Vader was destroyed, this Dark Assassin fled to the system of Camino

Vaders secret Assassin, Dark Wraith

Rumored to be a renegade Mandalore, Darth Vader trained this eceptionally remarkable swordsman to use a light saber in plans to overthrow Darth Sidious.

Although he possesses no Force capabilities, his skills with a saber have proven to be an overwhelming match for the remaining Jedi...."