Described as a Lovecraftian-looking alien with taut and leathery skin, Tor Valum was a Dark Lord of the Sith. As the script specifies him to be 7,000 years old by the time of the film, it's assumed that Valum was born approximately during the fall of the Old Republic. At some point of his life, Tor Valum went to train Darth Plagueis, a legendary Sith Master who had the power to control the midi-chlorians to keep the ones he cared for from dying, which is implied to have been learnt from Valum. However, Valum possibly felt ashamed or dissatisfied of Plagueis at the end of his training, as he would later state that such name meant nothing for him. However, Plagueis' apprentice Darth Sidious became aware of Valum's existence.
In the days leading up to the Battle of Endor, Darth Sidious recorded a Sith holocron for his apprentice Darth Vader, asking him to take Luke Skywalker to the Remnicore system so Tor Valum could train him into the ways of the Dark Side of the Force to harness the untapped power of Mortis, an ethereal realm within the Force which was supposedly a myth. However, Sidious' plans failed as Vader redeemed himself and killed him to save his son before dying from his injuries, fulfilling his destiny as the Chosen One and bringing balance to the Force.
Decades later, during the First Order-Resistance war, Vader's grandson Supreme Leader Kylo Ren finds the Sith holocron on Mustafar. After Palpatine's message plays out, however, the holocron blasts red lightning on Ren's face because it scans him and realizes that he isn't Vader, leading Ren to get a new iron mask, reminiscent to that of his grandfather, which he later destroys by throwing it off his castle to shatter on the ground.
Eager to find Tor Valum, Kylo Ren takes his TIE silencer to Remnicore at night and finds an ancient stone military fortress consumed by time, where he finds Valum on the courtyard. After getting threatened with death by Ren, Valum offers the conflicted Dark Side warrior to replace the deceased Supreme Leader Snoke as his new master so he can find Mortis and unleash its power for himself if he severs his past to not end up like all the previous Sith and Jedi. While training, Valum finishes Kylo's training by teaching him how to Force drain the Living Force from a three-tusked Gronk Boar, reducing it to a husk. Desiring more, Kylo enters into an ice cave near them after Valum tells him there's a vergence there. Inside the cave, Kylo Ren meets a Force vision of Darth Vader and engages him in combat only to be defeated by it.
Leaving the cave, an angry Kylo Ren asks Tor Valum for Mortis' location, but Valum refuses to tell him, deeming him unworthy of its power due his failure on defeating the Vader vision. Not taking a no as a response, the Master of the Knights of Ren uses the Force to hold Valum, delving into his mind to find Mortis' location as Valum implores him to release him, but his pleas fall on deaf ears. In a last attempt to convince Ren from sparing him, Tor Valum assures Ren that he has given him everything, something Ren agrees before draining him from all his Living Force, killing Valum and reducing him to a withered shell. However, in the end, Valum's training was four naught, as Ren was disowned as a Skywalker and ended up getting defeated once and for all by Rey Solana on Mortis, putting an end to his plans of conquest.
Colin Trevorrow presented his Duel of the Fates script to Lucasfilm in December 2016, which was read by both Star Wars creator George Lucas and actor Mark Hamill. Unfortunately, Carrie Fisher's unexpected death altered his plans and forced him to rewrite the script he had written with Derek Connolly, even asking playwright Jack Thorne to rewrite it. However, producer Kathleen Kennedy ultimately realized that Trevorrow wasn't the right person for the job during the initial scripting phase and ultimately fired him before rehiring J.J. Abrams, director of Star Wars: Episode VII - The Force Awakens, to direct the film, which was renamed Star Wars: Episode IX - The Rise of Skywalker and released in 2019. While the final version retained some elements from Trevorrow's script, Tor Valum wasn't one of them, as Abrams opted to brought back Emperor Palpatine as the main antagonist and tie him into Rey's origins.
- Tor Valum's existence in the Duel of the Fates story would have mainly contradicted the Rule of Two, a Sith philosophy revealed on Star Wars prequel trilogy which indicated that only two Sith Lords, a master and an apprentice, could exist at any given time. Taking this into account, Darth Plagueis would have had to slay Tor Valum if he took Darth Sidious as his apprentice. It doesn't explain as well why Tor Valum doesn't have the Darth title on his name or how Anakin Skywalker brought balance to the Force as the Chosen One if the prophecy meant the end of the Sith and Tor Valum was still alive. It's likely, however, that some retcons would have been established by Lucasfilm to resolve all these contradictions.
- Tor Valum would have canonically replaced Darth Tenebrous, the Sith Lord who trained Darth Plagueis in the Star Wars Legends continuity. Incidentally, Tenebrous was recanonized with the releasee of the visual dictionary of The Rise of Skywalker, but whether he remains Plagueis' master in the new Canon or not has yet to be established.
- In some ways, Tor Valum was conceived as a dark reflection of Yoda, as while Yoda trained Luke Skywalker in The Empire Strikes Back to become a Jedi Knight, Tor Valum would have trained Kylo Ren to become a Sith Lord. That said, this would have been yet another parallel of the Star Wars sequel trilogy towards the original trilogy.
- Had Colin Trevorrow's version of the film had been made, Tor Valum could have been easily considered as one of the two Greater-Scope Villains of the Star Wars franchise, alongside his apprentice Darth Plagueis. This is because Plagueis trained Darth Sidious, the franchise's main antagonist, into the ways of the Dark Side of the Force before Sidious killed him, and Sidious' backup plan if he was killed involved having Tor Valum training Luke Skywalker to become his successor.