Thus far, it’s heavily implied that the Knights of Ren were fellow students of Luke who rebelled to join Kylo. In the entry about Kylo Ren, Luke wrote about how his nephew “slaughtered” the Jedi students who refused to follow him to the Dark side.

In the canonical novel Star Wars: The Secrets of the Jedi, Luke Skywalker writes several journal entries chronicling the history of the Jedi. However, new evidence offers startling new details about the history of the Knights of Ren, and even hint at a Darth Vader connection we could see play out in The Rise of Skywalker. Their name has always been the primary indicator that the knights were under the leadership of Kylo Ren, even though we’ve yet to witness them working together in any of the new sequel films. Having only appeared in a flashback sequence in Star Wars: The Force Awakens, the elusive Knights of Ren remain one of the biggest mysteries of the sequel trilogy.