Created from one of the Emperor's favorite samples, B-2332-4, Luuke Skywalker was a clone of Jedi Knight Luke Skywalker. When Luke and Mara Jade found C'baoth in the throne room under Mound Tantiss, the Dark Jedi directed the clone to attack the young Knight.
Luuke Skywalker was defeated by Mara with his own lightsaber, actually Darth Vader's.