Luke Skywalker Secretly Learned Lightsaber Combat From a Stormtrooper
During Marvel Comics' 2015 run of Star Wars - set after A New Hope - it was revealed that Luke Skywalker surprisingly learned the bulk of his lightsaber combat skills from a stormtrooper. When the young Rebel went searching for answers about his Jedi path after the destruction of the first Death Star, he ended up being captured on the Smuggler's Moon of Nar Shaddaa, becoming the prisoner of Grakkus the Hutt, a Jedi-artifact collector. As a result, Luke was trained by the Hutt's gamemaster, who taught him the fundamentals of lightsaber combat to make him more entertaining for Grakku's fighting pits. However, it was later revealed that this gamemaster was actually Sgt. Kreel, an elite lightsaber-wielding stormtrooper working undercover for Darth Vader himself.
In Jason Aaron's run of Star Wars from 2015 to 2017 (alongside star artists such as John Cassaday, Simone Bianchi, Stuart Immonen, Mike Deodato, Mike Mayhew, Leinil Francis Yu, Jorge Molina, and Salvador Larroca), Luke was still struggling to figure out how he was supposed to become a Jedi, as there was only so much he was able to learn from his master Obi-Wan Kenobi before his death in A New Hope. As a result, Grakkus' gamemaster (and undercover stormtrooper) proved to be a great benefit, explaining the growth in Luke's abilities as a fighter in between the fourth and fifth episodes of the Star Wars saga. However, as soon as Sgt. Kreel's true identity was revealed, the hunt was on, and Kreel and his SCAR Squadron of elite troopers were relentless in their attempts to hunt down Luke and his Rebel allies.
Sgt. Kreel and SCAR served as consistent foes to the Rebels, and he and Luke in particular crossed lightsaber blades on more than one occasion. Additionally, Kreel wielding a green lightsaber resulted in a tenuous relationship with Darth Vader. While the Sith lord saw the value of Kreel's skills and his unwavering loyalty, he also held the stormtrooper to an extremely high standard, refusing to let Kreel be anything less than worthy of the blade he carried. Furthermore, every time Kreel fought Luke, he offered tips and advice on Luke's form, allowing the son of Vader to keep getting better and honing his skills while offering more of a challenge for Kreel each time they fought.
Interestingly enough, Sgt. Kreel and SCAR Squadron have not been seen since writer Charles Soule took over for Marvel's new 2020 run of Star Wars, which takes place after the events of Empire Strikes Back. As a result, it's possible that they could show up at some point down the line or in other media, offering Luke the chance to finally gain the upper hand now that he's had some significant training in the Force from Jedi Master Yoda.
There certainly seems to be more story to be told (or at least concluded) for Sgt. Kreel and SCAR Squadron, and hopefully they'll one day be brought back to resume their hunt for the Rebels. Regardless, the fact that a stormtrooper was instrumental in Luke Skywalker's training and evolution into a Jedi is as surprising as it is impressive in the Star Wars galaxy.