Erno was a detective in the Coronet City Peace and Security department following the Battle of Endor. Erno was divorced from his wife, who lived with a pair of artists in the Teeno Village district. He was posted at a Peace and Security station prior to the Coronet City revolution. Shortly before the Acolytes of the Beyond attacked Coronet City, Erno arrested a human youth named Remi, who called himself Oblivion. Erno caught the boy spraying an image of Darth Vader with the message "VADER LIVES" on the wall of the police station. Regarding the youth as a vandal, Erno took him into an interrogation room for booking.
When Remi expressed defiance and claimed that Vader lived, Erno pointed out that the former Sith Lord had perished about the second Death Star above Endor. Erno dismissed Remi's remark that death was not the end. When Erno asked the boy his name, Remi responded that he was called Oblivion. Erno then tried to offer the boy leniency if he would name his fellow Acolytes. When Remi remained silent, Erno dismissed 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 asked Remi why he did not wear a mask and suggested that the Acolytes were fans of Vader. Remi responded by asking Erno whether he was a decent man. Unwilling to let the boy pry into his personal life, Erno asked the boy about the mask again. Remi responded that the Acolytes had to earn their masks. Remi added that the building was very old and hinted that he knew that the Peace & Security station shared the basement with the library next door. Before Erno could continue the interrogation, the security officer Spob Rydel entered the interrogation room to inform Erno that the Acolytes were attacking parts of Coronet City.
When Rydel suggested roughing up their prisoner, Erno agreed and returned to the cell to fetch Remi. However, the prisoner had escaped. At that point, the lights went out. After the emergency lights had kicked in, Erno witnessed Rydel and the detectives Shreen and Mursey being gunned down by the Pantoran Kiza, another Acolyte who had disguised herself as a secretary. When Erno demanded to know what was going on, Kiza replied that she was not his doll. He tried to shoot her with his blaster but Remi returned and sliced off his blaster hand with an ancient lightsaber he had retrieved from the underground archives. Kiza then clubbed the wounded Erno in the head and told him that Vader lived and to tell the others that the Acolytes were coming.
Erno was a male Corellian detective who regarded himself as a scruffy thick-neck. Erno did not regard himself as a good person due to his estranged relationship with his wife, who had left him to live with two artists in the Teeno Village district. His neighbors regarded him as a slob. 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 regarded Darth Vader as a bad man and thought that he was a machine. Erno dismissed the Acolyte Remi's claim that Darth Vader still lived despite the Battle of Endor. He regarded the Acolytes of the Beyond as a group of criminals and trouble-makers. 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 knew how to wield a blaster.
Erno first appeared in Chuck Wendig's 2016 novel Aftermath: Life Debt, the second installment in Star Wars: The Aftermath Trilogy.