The Secret Apprentice, codenamed Starkiller, named Galen Marek was a Human apprentice of the Sith Lord, Darth Vader. When Darth Vader found him on Kashyyyk, he then was taken to be trained, by Vader, for many years to hunt down any Jedi that were found to have survived Order 66. With the help of a droid named PROXY and a group of pilots. Vader also hoped to eventually use his Apprentice to help overthrow Palpatine one day. But it was revealed in The Force Unleashed that Vader never planned to use him to overthrow Palpatine when he first found him until later on.