In Star Wars VII: The Force Awakening, Kylo Ren was the student of Supreme Leader, Snoke. He was the de-facto leader of the First Order. To be a better boss and understand who his coworkers feel, he decided to go undercover as a radar technician named Matt. At first, he was uneasy for the role and seems obvious that he was Kylo Ren. For a guy with a big ego to become a low-level worker. Throughout the debacle, he befriended a storm-trooper and a supervisor. It turns out that Kylo Ren killed the supervisor’s son. In the end, it turned out that everybody knew he was Kylo Ren. He ended up killing the supervisor.
You can catch Kylo Red again in Star Wars: The Rise of Skywalker