While Darth Vader had a secret apprentice in Legends, there’s a good reason why he didn’t have one in the official Star Wars canon before trying to get Luke Skywalker to join him. As Emperor Palpatine’s apprentice, Darth Vader tried multiple times to replace his master (according to the Sith’s Rule of Two). However, he never trained an acolyte.

Compared to the rest of the Empire hierarchy, Vader was very much an anomaly. However, this was intentional and by design. Despite having authority, Palpatine’s Imperial system deliberately kept Vader on the outside to limit his power. However, changes to Vader’s Imperial status can explain why he started making moves against Palpatine and tried to make Luke his apprentice.

The Imperial System Began To Fail By Rogue One

From the moment the Empire rose to power in the aftermath of Revenge of the Sith, Darth Vader was given command of the Imperial Inquisitors, tasked with hunting down any surviving Jedi. In effect, this arguably kept Vader away from the Empire proper, while also preoccupying the two biggest threats to Palpatine’s power: the Jedi and his own Sith apprentice.

After all, both Vader’s castle and the Fortress Inquisitorius were located far away from the Imperial center of Coruscant. However, the Empire began showing cracks of instability by Rogue One and A New Hope.

This, functionally, is the real reason for Vader’s cameo in Rogue One and leading role in A New Hope – he’s brought in because the Empire has failed to contain the Death Star plans, combined with a leadership vacuum amid the official Imperial hierarchy.

The Empire ends up losing the two critical leaders and tacticians Palpatine believed could’ve contained the Rebellion; Thrawn beforehand in Star Wars Rebels, and then Tarkin in New Hope, not to mention so many other key Imperials (like Project Stardust’s Director Krennic and the ISB’s Admiral Partagaz).

Darth Vader Finally Found His Place By Empire Strikes Back

The Empire Strikes Back makes things pretty obvious. Now, Darth Vader is the one leading the charge on the front lines, as seen during the Battle of H๏τh. In the wake of the Death Star’s destruction, Vader is now the one going after the Rebellion in full.

The failure of the Imperial system meant Vader became the primary point-man, the leader, the primary enforcer (Force-choking any who failed him along the way). From that moment on, Darth Vader was much more active within Palpatine’s Imperial machine.

By this point, Darth Vader is no longer going after Jedi survivors on the fringes of the galaxy, and the Imperial Inquisitors are no longer in operation during the Galactic Civil War either.

This is proven in the canon comics set between the events of the original trilogy movies, as well as in games like Star Wars Outlaws, where Darth Vader is shown receiving direct reports from the Imperial Security Bureau and their clandestine operations within the galaxy’s criminal underworld and its various crime syndicates.

These same transitional stories also show Vader becoming bolder, as it’s after the Death Star’s destruction that he presumably starts feeling more respect and fear from the Imperial hierarchy than ever before, even if it did come with unique consequences (like a secret Imperial cabal dedicated to killing Vader between Empire Strikes Back and Return of the Jedi).

Nevertheless, it does make sense that Darth Vader becoming a more integral part of the Imperial machine helped motivate his decision to start plotting to replace Palpatine.

Darth Vader Never Believed He Could Defeat Palpatine On His Own

On the other side of that coin, it’s notable that Darth Vader still believed he needed Luke to truly defeat Emperor Palpatine.

It’s been made clear in the official Star Wars canon that Vader desperately wanted his son to join him, and a driving force was likely to be reunited with a part of his family he’d long thought gone. However, the other part of it was that Vader firmly believed he wasn’t strong enough to take on Palpatine by himself.

Having perhaps lost so much confidence in the face of Palpatine’s great power and being kept outside the primary Imperial hierarchy for so long, Vader did not believe he could kill Palpatine on his own, especially after he tried and failed multiple times before in the established canon.

Sure, it would have been cool to have seen Vader training an apprentice in secret, just like in Legends with The Force Unleashed’s Galen Marek aka Starkiller. Perhaps Vader could have found an Inquisitor with great promise in the dark side to forge into his secret acolyte.

However, the reality of the official Star Wars timeline is that Vader was not bold enough to move against his master until the middle of the original trilogy.

By that time, Luke Skywalker was a known enтιтy, explaining why Darth Vader’s attempt to bring his son over to the dark side was the first time he even tried to gain his very own apprentice.