What is the name of Darth Vader's secret apprentice?
Galen Marek, codenamed Starkiller, a Dark Side Adept who was selected by Darth Vader to help him during the Great Jedi Purge. He was selected because he had the greatest Force Potential ever (even more powerful than the Emperor and even Anakin in his prime). He was deceived several times by Vader and then used by him to flush out the Emperor's enemies. The whole thing backfired because Galen ended up organizing what would eventually become the Rebel Alliance. The symbol for the Rebel Alliance is the Marek family crest.