At some point before 0 ABY, Darth Vader visited ancient Jedi ruins on Dantooine which housed an active, yet unmanned, cloning facility. He was ambushed by security turrets and his squad was all killed. Vader was injured during this visit and some of his blood was left in the facility.
Believing that they were properly executing their programming, the experimental cloning droids running the facility created a clone of Vader using this sample. The droids then applied a mysterious technique (used with all of the facility's clones) in which they imprinted the clone with Vader's personality (from mental imprints left by the original host).
However, as with the other clones from the facility, this process was faulty and left the clone with only partial mental functioning and personality synchronization. This notion seems to explain why the clone was unable to utilize the full Force potential of its presumably uninjured, four-limbed body in its later fight against the real Darth Vader, who had not held such a physical state since before his fateful duel with Count Dooku in 22 BBY.
Despite apparently not requiring armor similar to Vader's, the clone was dressed in a costume accurately reflecting the detail, but without the functionality of Darth Vader's armor. Tash Arranda deduced that it had been constructed from scrap lying around the abandoned Rebel base on Dantooine. The clone Vader also had a lightsaber, however, like the armor it was merely an imitation, producing a fake blade that simply passed through objects without inflicting any damage.
Darth Vader returned to the facility in 0 ABY, soon after Tash Arranda, Zak Arranda, and Mammon Hoole visited there. Vader slew his clone in battle and briefly contemplated its nature before departing the facility.
- Galaxy of Fear: Clones (First appearance)