Carbonite Sith Master
From Wookieepedia, the Star Wars wiki.
This unknown Sith was frozen in carbonite and placed in a tomb along with the Carbonite Sith Army. His life support monitors showed that his vital signs were good, and that the Sith was still alive.
Next to the block of carbonite holding the Sith sat an urn, whose contents were unknown. Lying in a simple stand at the top of the urn was a lightsaber.
The identity of this Sith and the reason why he and the Sith Army were encased in Carbonite are not known.
[edit] Behind the scenes
While not actually seen in the cutscene that reveals the army, the game files include this entry as "Carbonite Sith Master".
