With most of the Star Wars fan enthusiasm focused on The Last Jedi right now, it's easy to forget that we have years of non-saga films to look forward to — we know that a #HanSolo standalone film is in development, but what other adventures could we see?
Rogue One was a perfect example of a Star Wars story that can stand on its own, while at the same time being interconnected with the mainstream universe. And seeing as how the movie was a huge success, Lucasfilms would be smart to apply its dynamic to future films. A perfect story for such an adaptation would be Galen Marek's.
The name Galen Marek might not sound all that familiar because he hasn't been featured in the mainstream Star Wars universe. Marek plays a pivotal behind-the-scenes role in the de-canonized Legends lore, but he hasn't made a cinematic appearance — only appearances in 2008-2010 video games such as Soulcalibur IV, Star Wars: The Force Unleashed (which tells his complete story) and Star Wars: The Force Unleashed II (in which he's cloned), along with an associated comic book, novel and toys.
Darth Vader's Apprentice
In the Star Wars canon, Galen Marek was the son of two well-known Jedi. Their family, having strong connections to the Force, were pursued by the Sith. Darth Vader himself killed Galen's parents and took Galen as an apprentice, giving him the name Starkiller (no official connection to Starkiller Base in The Force Awakens — that we know of yet).
Once Galen was ready to take on the difficult missions that Vader had planned for him, they received an unexpected visit from the Emperor, who didn't look too kindly on Vader taking on an apprentice. In response, the Emperor demanded that Vader kill Galen. Which he does — sort of.
Vader stabs Galen with a lightsaber and then revives him shortly after the Emperor leaves. When Galen awakes, Vader attempts to convince him that faking his death was the only way to keep the Emperor off their trail, but Vader has other plans in mind.
Darth Vader double crosses Galen in the end, but Galen defeats him. Unfortunately, Palpatine steps in and makes sure that Galen doesn't win. Unable to defeat the Emperor and Vader, Galen sacrifices himself in an attempt to stop them from causing any more harm, but obviously fails.
Could Galen Marek's Story Be Adapted Into a Movie
Now, Galen Marek's story doesn't end there — as mentioned before, he's cloned in the sequel game and even shows up in Lego Star Wars III: The Clone Wars — but his story is definitely one that could find its place within the new Star Wars canon, just like Rogue One. And it would be an ideal way to give us more Darth Vader on the big screen.
Not only would Galen be the first depiction of a trained Force user who isn't labeled as a Jedi or a Sith, his role could open the door for more Force users who follow neither the restrictive path of the Jedi nor the power-hungry drive of the Sith.
Galen Marek is the perfect candidate to center a standalone film (or multiple films) around. Marek's history depicts him on many missions, any of which could fill the duration of a feature-length movie. Plus, Marek's origins foretell his encounters with several known Jedi masters whom he fought and killed, so those potential scenes would definitely be something fans would want to see.
Starkiller is a beloved character, and the time has come to reintroduce him to Star Wars canon. As for actos who could portray him, we would definitely have to turn to Sam Witwer whose likeness was used for Starkiller in the games.