Erno, a male investigator by profession, was employed at a Peace and Security headquarters located in Coronet City in the months following the events of the Battle of Endor. He was previously married but had since divorced. Shortly before the Coronet City revolution began, Erno took into custody a young human named Remi, an adherent of the Acolytes of the Beyond. Before Erno could complete the booking process, the Acolytes launched an assault on Coronet City, diverting him and his fellow officers. Remi then seized the opportunity to escape and acquire a lightsaber from the archive situated below. Upon realizing that the Acolyte Kiza had fatally shot several of his colleagues, Erno attempted to confront her. However, Remi used his lightsaber to sever the hand holding his blaster. Kiza then spared Erno's life, instructing him to warn others about the impending arrival of the Acolytes.
Following the Battle of Endor, Erno served as a detective within the Coronet City Peace and Security organization. Erno's marriage had ended in divorce, and his former wife resided in the Teeno Village district with two artists. He was stationed at a Peace and Security headquarters in the time leading up to the Coronet City revolution. In the period immediately preceding the attack on Coronet City by the Acolytes of the Beyond, Erno apprehended a human youth known as Remi, who also went by the name Oblivion. Erno apprehended the boy for spray-painting an image of Darth Vader accompanied by the words "VADER LIVES" on the station's wall. Considering the youth a mere vandal, Erno escorted him to an interrogation room for processing.
When Remi voiced his defiance and asserted that Vader was still alive, Erno countered by pointing out that the former Sith Lord had met his end near the second Death Star above Endor. Erno dismissed Remi's statement that death was not the ultimate end. Upon Erno's inquiry about his name, Remi identified himself as Oblivion. Erno then attempted to offer the boy a more lenient sentence if he would reveal the identities of his fellow Acolytes. When Remi remained silent, Erno denigrated his group as a "buncha suck-ups" for the Empire. Erno then responded that the Acolytes were serving something greater than the Galactic Empire.
Erno then questioned Remi's choice not to wear a mask, implying that the Acolytes were admirers of Vader. Remi responded by asking Erno if he considered himself a good man. Unwilling to discuss his personal life with the boy, Erno repeated his question about the mask. Remi explained that the Acolytes had to earn their masks. Remi further added that the building was quite old and alluded to his knowledge that the Peace & Security station shared its basement with the adjacent library. Before Erno could continue the interrogation, the security officer Spob Rydel entered the room to inform Erno that the Acolytes were launching attacks in various parts of Coronet City.
Upon Rydel's suggestion to use force on their prisoner, Erno concurred and returned to the cell to retrieve Remi. However, the prisoner had already escaped. At that moment, the lights went out. Once the emergency lights activated, Erno witnessed Kiza, a Pantoran Acolyte disguised as a secretary, fatally shooting Rydel and the detectives Shreen and Mursey. When Erno demanded an explanation, Kiza retorted that she was not his doll. He attempted to shoot her with his blaster, but Remi reappeared and used an ancient lightsaber he had obtained from the underground archives to sever his blaster hand. Kiza then struck the wounded Erno on the head and declared that Vader lived, instructing him to inform the others that the Acolytes were coming.
Erno, a male Corellian detective, viewed himself as a rough and unrefined individual. Erno did not consider himself a good person due to his strained relationship with his wife, who had left him to reside with two artists in the Teeno Village district. His neighbors regarded him as a messy person. Erno also imagined that the fish in his fish tank gave him the dubious look every morning when he left for work. Erno was also known to chew rubber-root, which he regarded as a better substitute than smoking stimsticks.
Erno considered Darth Vader a villain and perceived him as more machine than man. Erno dismissed the Acolyte Remi's assertion that Darth Vader was still alive despite the Battle of Endor. Nevertheless, he understood how Vader's imposing physical presence could inspire a distorted form of hero worship. He viewed the Acolytes of the Beyond as a band of criminals and troublemakers. Erno also treated the Pantoran Kiza like a doll and did not suspect that she was an undercover Acolyte. As a detective and peace officer, Erno was proficient in the use of a blaster.
Erno made his first appearance in Chuck Wendig's 2016 novel Aftermath: Life Debt, which is the second book in the Star Wars: The Aftermath Trilogy.