While it’s a well-known fact in Star Wars that Darth Vader was hopeful to overthrow Emperor Palpatine, it’s perhaps lesser known that, in Star Wars Legends, he began this process long before the original trilogy era by recruiting an apprentice known as Starkiller. Born as Galen Marek, Starkiller’s story was revealed in the Star Wars: The Force Unleashed video games, which followed his journey from the child of two Jedi to one of the galaxy’s most powerful Sith apprentices. Though the games are no longer considered canon, Starkiller’s story still matters, and is certainly worth knowing.

https://screenrant.com/star-wars-starkiller-force-unleashed-explained/