The individual known as Sixth Brother, who previously went by the name Bil Valen, was a male humanoid belonging to the Inquisitorius. In the year that came after the Clone Wars concluded, the Sixth Brother, along with the other Inquisitors, were tasked with hunting down Force-sensitive children and Jedi who had managed to survive Order 66. He accompanied Darth Vader, together with the Ninth Sister and the Tenth Brother, to the planet of Mon Cala with the purpose of hunting down an enemy of the Empire. He met his death at the hands of Ahsoka Tano during the uprising that occurred on Raada.

Bil Valen, who was a humanoid man, was initially a part of the Jedi Order. At some point in time, he was brought into an Imperial organization consisting of fallen Jedi assassins known as the Inquisitorius and was then given the title of Sixth Brother. The Inquisitorius had the responsibility of tracking down and eliminating any Jedi who had lived through Order 66. In order to achieve this goal, he and his colleagues received training from the Grand Inquisitor at the Inquisitorius Headquarters situated in The Works.
The Inquisitorius soon came under the control of Darth Vader when Darth Sidious initially presented the Inquisitorius to Vader. Darth Vader proceeded to further their education in the ways of the dark side of the Force, instructing them to employ more aggressive strategies and less defensive approaches than what they had learned during their time with the Jedi. The Sixth Brother engaged in a training session with Vader, during which the Sith Lord cut off his lower left arm to impart the lesson of loss upon him. The Grand Inquisitor inquired with Vader about his reasons for training the Inquisitors in this manner, to which he disclosed his intention to enhance the aggressiveness of their fighting techniques.

In the year 18 BBY, the Sixth Brother, along with the Ninth Sister and Tenth Brother, went with Vader and a group of Purge Troopers to Mon Cala for a mission aimed at finding a rumored Jedi who was said to be advising the King of Mon Cala during negotiations with the Empire. Upon their arrival, the Tenth Brother commented that the planet smelled like fish, and the Ninth Sister joked that the smell was just Sixth Brother. Sixth Brother responded with a sarcastic compliment, and the Ninth Sister stepped forward to speak with Gial Ackbar, the King's chief of security. Vader then took over from the Ninth Sister, and an Imperial shuttle exploded nearby. Vader led the three Inquisitors into Dac City to begin their search.
After a significant battle erupted between the Empire and the Mon Cala in Dac City, the Sixth Brother and his fellow Inquisitors took part in the conflict as they chased after King Lee-Char to the Dac City palace in order to discover the whereabouts of the Jedi who was advising him. Eventually, they managed to enter the palace after killing numerous Mon Calamari and Quarren defenders, and the Ninth Sister began to interrogate Lee-Char. However, before long, a horde of large creatures emerged from the depths and created massive waves that swept across the surface, overwhelming the Imperials. Sixth Brother and the others attempted to withstand the waves, but they were not strong enough, even with Vader's assistance.

Fortunately, the Sixth Brother and the other two Inquisitors survived and used an Imperial submarine to locate Vader. After picking him up, the Ninth Sister informed Vader that she had discovered the Jedi's location, and they proceeded towards it in the submarine. The submarine took them to the location where the Jedi and his six acolytes were evacuating their refuge. The group immediately dispersed, except for one acolyte who attacked the submarine, only to have his helmet crushed by Vader. As the others swam away, the submarine pursued them, and another acolyte sacrificed himself to slow it down.
The submarine arrived at Bel City, where two more acolytes were waiting to ambush them. Vader led them through the hallways, where he received an order from Moff Wilhuff Tarkin instructing him to capture Lee-Char. The other Inquisitors, supported by the Purge Troopers, continued the chase. They found the Jedi and his last two acolytes, and the Sixth Brother struck down one of them with his lightsaber. He then inquired about what Barr had said earlier, and the Tenth Brother, claiming his hearing was exceptional, stated that Barr had said there was no way out. Sixth Brother and the other two Inquisitors, backed by their Purge Troopers, then surrounded the Jedi and his last acolyte, Verla.

With no other option, the Jedi confronted the Inquisitors but then began to mention their original names from their time as Jedi. The Ninth Sister recognized the Jedi and revealed his name, Ferren Barr, stating that he was still just a Padawan who lacked the necessary training to defeat them. Barr ignored her insults and continued, explaining the role of the clones in Order 66 and pointing out that the Purge Troopers had been activated after Order 66 was initiated. After this, the Sixth Brother aimed his lightsaber at Barr, but Barr reiterated that they were still Jedi and used a mind trick on the Purge Troopers, instructing them to "execute Order 66."

The troopers were deceived by Barr's trick and turned against the Inquisitors. The Tenth Brother protested that they were not Jedi, but it was too late. The troopers opened fire on them, forcing the Inquisitors to deflect their shots. The Tenth Brother was struck in the chest and killed. Barr and Verla then leaped over the battle and escaped. Eager to intercept them, the Sixth Brother suggested to the Ninth Sister that they do the same. The Ninth Sister proposed moving the troopers out of the way instead, and they both used the Force push to shove the troopers aside. However, in an effort to ensure his own safety, the Sixth Brother betrayed the Ninth Sister, severing her leg and leaving her to fend off the remaining troopers. After his escape, the Sixth Brother boarded a boat with three stormtroopers and passed numerous creatures that had been killed during the fighting on Mon Cala.
At a later time, the Sixth Brother came across surveillance holos and reports that indicated a Force-sensitive child was present on the planet Thabeska. He traveled to the Outer Rim world to investigate, but he was unable to find the child, Hedala Fardi. While he was on Thabeska, the Brother received a message from a low-ranking district commander on the moon of Raada. The report stated that a Force-sensitive individual, old enough to have undergone Jedi training, was active on the remote moon. Preferring a more challenging target and noticing that no other Inquisitor had responded to the message, the Sixth Brother decided to go to Raada to investigate the possible Jedi.

The Sixth Brother made his way to Raada in order to hunt down the Jedi that had been sighted on the small agricultural moon. He found out from Jenneth Pilar, an information broker who was collaborating with the Empire on the moon, that a Jedi or Padawan had been involved in an uprising carried out by the local farming community. During the uprising, a teenage farm worker named Kaeden Larte had been captured and tortured in an attempt to extract information. The Brother scoffed at the methods that were used on Larte, as they proved to be ineffective. He learned that Kaeden had then been rescued from the Imperial base by a Force-sensitive being.
The Brother tracked down Kaeden and the other farm workers, who had sought refuge in a series of mountain caves located not far from the settlement. Kaeden surrendered herself to the Inquisitor, but her friends soon launched an attack on him. The Brother deflected the blaster bolts fired by the farmers, killing them in the process. As a display of his power and to intimidate them, the Brother hurled his lightsaber at the Rodian farmer, Kolvin, instantly cutting him in half.
In order to lure the Jedi back to Raada, the Brother arranged for footage of himself holding Kaeden prisoner to be leaked. Upon seeing the footage, Ahsoka Tano returned to Raada, having already made arrangements for the evacuation of the moon's population. She was in the process of constructing a new pair of lightsabers, and she could hear the kyber crystals within the Brother's double-bladed lightsaber calling out to her. Despite the fact that she did not have her own lightsabers, Tano was able to hold her own against the Sixth Brother and eventually used the Force to extract the crystals from within his lightsaber just as he was attempting to deactivate its spinning function. The lightsaber became unstable and exploded right in front of his face, resulting in the Sixth Brother's immediate death. Ahsoka then proceeded to purify the lightsaber crystals from his weapons, cleansing them of the dark side energy that had tainted them, and used them to complete her new lightsabers.

The Sixth Brother belonged to a humanoid species that neither Kaeden Larte nor Ahsoka Tano were able to identify. He was tall, slender, and had broad shoulders, with skin that appeared unnaturally gray, piercing ice-blue eyes, and uniform markings that resembled scars on his cheeks, nose, and chin. Similar to his fellow Inquisitors, he wore black and gray body armor and carried a double-bladed spinning lightsaber. He also wore a helmet with a blast shield that could be lowered to provide protection for his face.
The Sixth Brother had a complex relationship with his fellow Inquisitors, as he feared competition from them. Upon arriving on Mon Cala, the Ninth Sister and Tenth Brother insulted him, to which he responded with sarcastic compliments. When picking up Darth Vader beneath the oceans of Mon Cala, the Sixth Brother assumed that Vader would be grateful for it, but Vader simply stated that he could handle himself. During the battle in Bel City, the Sixth Brother was eager to pursue Ferren Barr and attempted to jump to conclusions about what he and the Ninth Sister would do. After pushing away the Purge Troopers, the Sixth Brother betrayed the Ninth Sister and severed her leg so that she would be forced to hold off the remaining troopers. When the Ninth Sister threatened to kill him, he mockingly wished her good luck, telling her that she had always been his favorite.
The Sixth Brother was ruthless and felt completely at ease with the idea of killing innocent beings, even children. He also despised the aspects of his mission that prevented him from acting in such a manner. He was known to enjoy the prospect of facing more challenging prey, which was the primary reason he abandoned his task of tracking a Force-sensitive child in favor of hunting Ahsoka Tano. He was also arrogant, proclaiming himself to be "the future" and displaying overconfidence during his fight with Tano, which ultimately led to his demise.
The Sixth Brother received training from Darth Vader, the Dark Lord of the Sith. Vader trained him to abandon the defensive tactics he had developed as a Jedi and instead rely primarily on offensive tactics. His training proved to be successful, as he killed many Mon Calamari during the occupation of Mon Cala. His life extended beyond the Tenth Brother, who was unable to hold off the Purge Troopers when they turned against them. He displayed very little in the way of his powers and abilities during his hunt for a Force-sensitive child on Thabeska, as well as his confrontation with Ahsoka Tano. Tano described him as "lacking finesse" and "relying mostly on brute strength," and he was also apparently unable to fight with his helmet's blast shield down. Despite this, he was able to both deflect blaster bolts back at their firers and throw his saber in order to chop Kolvin in half. He also did this to a disciple named Daren while on Mon Cala.

The Sixth Brother possessed a double-bladed spinning lightsaber that could be thrown like a boomerang. He wore a blue helmet with a neck guard that drooped down the back and a silver and black face shield that was always lowered to cover most of his face. The Sixth Brother's suit was silver, and over it, he wore black armor on his shins, upper chest and shoulders, and forearms. He wore a black kama around his waist, and his armor had red attachments around it.
The Sixth Brother made his first appearance as the main antagonist in E. K. Johnston's 2016 novel Ahsoka. He was first depicted in Darth Vader (2017) 6, although it was not confirmed that the Inquisitor was him until Darth Vader (2017) 7. In Darth Vader (2017) 16, the former names of the Sixth Brother and Ninth Sister were revealed to be Bil Valen and Masana Tide, although the comic did not specify which character had which name. The Sixth Brother was confirmed to be Bil Valen in the 2018 reference book Star Wars: The Dark Side.
According to Dave Filoni, the Star Wars: Tales of the Jedi episode "Resolve" portrays the same events as the Ahsoka novel, which would logically imply that the inquisitor featured in the episode is the Sixth Brother. However, there are numerous differences between the short and the novel. Additionally, upon seeing the trailer for the series, Johnson assumed that the Inquisitor was not the Sixth Brother featured in her novel. The reference book Star Wars The Dark Side Pocket Expert later included information from Tales of the Jedi but stated that the Sixth Brother had only appeared in novels and comics up to that point, logically meaning he was not featured in the Tales of the Jedi episode, meaning it depicts separate events. The novel Inquisitor: Rise of the Red Blade, which was released after Tales of the Jedi, featured the Sixth Brother but described him in a way that matched Ahsoka, not the Tales episode, with blue eyes. Eventually, Star Wars Insider 229 identified the Tales Inquisitor as the Eleventh Brother, definitively separating him from the Sixth Brother, despite the similarities between their encounters with Tano.