Ren was a Force-sensitive being who functioned as the leader for the Knights of Ren, a group of practitioners of the dark-side. This individual brandished a lightsaber with a red blade, also known as the Ren. By the year 3 ABY, some believed that a human individual had killed Ren to take the Knight's lightsaber and Ren's name.
Sometime between 3 ABY and 4 ABY, the Knights, then under the leadership of Ren's replacement, carried out a heist at the castle of the Dark Lord of the Sith Darth Vader on Mustafar, an Outer Rim planet. During this event, the human "Ren" engaged Darth Vader in a duel with the Ren lightsaber. Upon seeing the Knight with the red lightsaber, the Sith declared Ren unworthy of wielding the weapon; Ren refused this judgement, stating that Vader was not the one to determine his worth. Ren proceeded to tell the Sith that he had earned everything he possessed, including the lightsaber he had taken from his predecessor.
The first mention of Ren occurred in the fourth issue of the 2021 comic miniseries titled Star Wars: Crimson Reign. Charles Soule wrote the issue, and Marvel Comics published it on April 27, 2022.