WARNING: The following contains spoilers for Star Wars: Age of Rebellion -- Darth Vader from Greg Pak, Ramon Bachs, Stephane Paitreau and Travis Lanham, on sale now.

It's no secret Emperor Palpatine put Darth Vader through rigorous tests in the Star Wars Universe and, more often than not, they secretly drew the ire of the fallen Jedi. However, despite each test, as frustrating as they may have been, as the Original Trilogy illustrated, Vader was mostly willing to put up with anything and everything thrown at him.

RELATED: Star Wars: Age of Rebellion Reveals the Galaxy's Most Prized Commodity

However, Marvel's latest Age of Rebellion one-shot finally offers insight into Vader's greatest test -- one which certainly tested his patience as understudy to Palpatine and almost drove him to lose his composure.

This story, "To The Letter," focuses on Vader's silent feud with Governor Ahr, who complained about him after Vader blew up insurgents on Namzor in the Mid Rim. Ahr wanted the coaxium they were stockpiling, but Vader's actions cost him a reservoir of this precious fuel. Shockingly, Palpatine admonishes Vader in front the bureaucrat, insisting he obey Ahr because, by serving this man, Vader's serving Palpatine's will.

It's clear he's trying to teach Vader a lesson and says in due time he'll understand what that lesson is, but clearly, the master is striking at his apprentice's ego. And so, Vader is put through a series of Herculean tests by Ahr, with suicide missions in Ahn Krantarium in the Mid Rim against deadly robots and more insurgents in Phelzepham pushing Vader to the brink. But each time he returns, he has to bite his tongue, with the most he can do being flashing his crimson lightsaber just to show he is ticked off.

RELATED: Marvel's Star Wars Comic Fills a Major Last Jedi Plot Hole For Luke Skywalker

It comes to a head in Kankalo Belt Containment Zone when Vader is tasked with navigating an asteroid belt to find the greatest threat he could and destroy it. It's once more Ahr's way of covertly trying to get him killed, however, Vader flies back to the ship without any prize. When Ahr questions him, a lobster-like monster attacks the wing and kills him, with Vader avoiding the damage due to the Force. At this point it's apparent the lesson wasn't to obey Palpatine or some middle manager, it was about finding a way over obstacles -- in this case, Vader's narcissism.

Palpatine takes pleasure in Vader overcoming his pride, but it's also a win-win because once his hubris is cut down, he becomes a better and more docile servant to the dark overlord. However, watching Vader go through these motions isn't easy because he really is brought down to the level of an average soldier, akin to a Stormtrooper. It's something you can tell annoyed him, but he had to follow through because his boss simply willed it. To make things worse, Palpatine lets Vader know that as much as he hates going through this, he will savor every moment of it because he loves seeing his protege squirm.

It's pretty twisted and honestly recalls all the tests we saw Vader endure in Star Wars Rebels and other Marvel books. At least in those cases, he would take direction from esteemed colleagues and men he could respect, like Grand Moff Tarkin. Here, though, Ahr isn't even on Admiral Thrawn's level. He's a simpleton, greedy and looking to just collect trophies for Palpatine, with no strategy or intelligence to really make a difference for the Empire.

RELATED: Marvel's Star Wars Comic Reveals Lando Calrissian's Secret Missions

Vader found a solution for his predicament, but ultimately, it once more proved why his relationship with Palpatine always stood on rocky ground. You can only push someone so far before they break, and in Vader's case, that point meant throwing his boss into a reactor to kill him so the galaxy could finally be free of Sith tyranny.