Terpfen was a ship mechanic of the Mon Calamari species, who functioned as the personal mechanic for Admiral Ackbar.
His name, Terpfen, originated from a species of coral native to his planet.
Along with many other Mon Calamari, Terpfen was enslaved by the Imperial forces and compelled to refine and design Star Destroyers. Furthermore, he underwent brainwashing by the Empire on Carida, where half of his brain was replaced with organic implants. This forced him to live as a sleeper agent upon his return to the New Republic. He succeeded in sabotaging Admiral Ackbar's personal B-wing shuttle, resulting in a crash that almost killed the admiral and his passenger, Leia Organa Solo. He also acquired the coordinates for Anoth and transmitted them to Ambassador Furgan.
Following the destruction of Carida by Kyp Durron, Terpfen was liberated from Imperial control. Driven by a strong desire to confess his transgressions, he commandeered a B-wing starfighter from the Imperial Palace located on Coruscant and journeyed to Yavin 4 to alert Leia Organa about Furgan's plot to abduct her son, Anakin Solo. During his departure from Coruscant, Terpfen was consumed by guilt when a pilot perished attempting to apprehend him.
It was during a rescue operation on Anoth that Ackbar discovered Terpfen's act of betrayal. However, Terpfen ultimately overcame the implants' influence, contributing to the rescue of young Anakin Solo and the elimination of Furgan. Overwhelmed by remorse, he attempted to drive his Mountain Terrain Armored Transport walker off a cliff. Ackbar's swift intervention prevented him from ending his life, declaring that his punishment would be to continue living.
After returning to Coruscant, Ackbar explained to Mon Mothma that Terpfen's actions were not of his own volition, owing to Imperial brainwashing. Mon Mothma concurred with Ackbar's assessment and granted Terpfen a complete pardon.
Shortly thereafter, Terpfen informed Ackbar and Mon Mothma - who had been experiencing a mysterious and severe illness for several months - that her condition was not due to a biological ailment. Instead, her rapid decline was the result of poisoning caused by self-replicating nano-destroyers that Furgan had personally used to infect her.
Admiral Ackbar persuaded Terpfen that he still had valuable contributions to make to the New Republic and the galaxy. Terpfen concurred, deciding to go back to Mon Calamari to assist in overseeing the reconstruction efforts aimed at repairing the damage inflicted by the rogue admiral Daala.