Arn Peralun was a cyborg male Human Jedi Knight. He served the Jedi Order during the third war, which was fought with the reconstituted Sith Empire. He became Tau Idair's Padawan after 3627 BBY.
While with his master on Dakot Seven, artillery fire severely injured Arn when he tried to defend the local population from slavers. Arn survived, but his master did not. The inhabitants of Dakot Seven were not biologically compatible with Kolto or Bacta, so they used cybernetics to heal Arn, which was the only method they knew. Over eighty percent of Arn's body was augmented and replaced to keep him alive.
His recovery process took years, delaying his Padawan training and making him one of the oldest padawans in the order. However, Master Gnost-Dural took an interest in the Padawan and assigned him to the Jedi Knight Tau Idair to continue his training.
Gnost-Dural dispatched Peralun alongside the Commander of the Eternal Alliance to Onderon to meet his new master. Upon their arrival, Peralun was introduced to the Sith Lana Beniko before he and the Commander were able to meet with Idair. After he met his new master, an explosion nearby prompted the three to investigate. Peralun correctly identified Darth Savik's presence on Onderon, which allowed the Republic to coordinate with Senator Deja Nebet and foil the Sith Empire's plans for the planet.
Following their successful disruption of the Sith's forces on Onderon and the capture of Savik, Peralun accompanied his master to Mek-Sha. The Republic successfully achieved its objectives there while diminishing the Sith's influence over the colony.
However, Peralun's past encounters with slavers on Dakot Seven motivated him to hunt down the Brothers, a slaver group. Peralun succumbed to his anger and killed the slavers without his master's knowledge. Idair and Gnost-Dural later stated that Peralun felt remorse for his actions, but they also acknowledged that he had yielded to his anger and prejudice.
After his setback on Mek-Sha, Peralun accompanied the Republic to Corellia to protect the Meridian Complex. There, he and his master confronted the Sith Lord Darth Malgus. The complex was saved, and Malgus was defeated (though he survived), but both master and pupil were nearly killed and required treatment for their injuries. The pair were saved by the Jedi Knight Kira Carsen and Scourge, who were seeking the Commander's help.
Peralun later became a member of Task Force Nova, a joint military-civilian effort in partnership with the Alliance to reunite Jedi scattered throughout the galaxy and establish a new homeworld. While traveling with General Daeruun's fleet to Odessen, they had to respond to a distress call from a refugee ship being attacked by the Dire Skulls. After driving off the pirates, Peralun and Idair pursued them. By this time, Idair and Gnost-Dural believed Peralun was almost ready for his Jedi Knight trials, a thought that both excited and terrified him.
Peralun later went with the Commander and Aryn Leneer to the Dantooine Jedi Enclave to investigate Darth Malgus's whereabouts. When they reported their findings to Gnost-Dural, Sal-Deron, Tau Idair, and Vinyor Tesh, Peralun defended Leneer when Tesh wanted her removed from the meeting because she was no longer a Jedi and therefore not entitled to the Jedi's affairs. Peralun collaborated with Tesh to discover that the artifact Malgus stole from Dantooine had once belonged to Darth Nul, but its properties and Malgus's intentions remained a mystery.
In the Republic storyline of Legacy of the Sith, players of either sex can flirt with Arn at a couple of points: once after rescuing him from his wrecked ship, and again after defeating Major Dosk, saying that they "enjoy his company". Later, Arn sends the player an in-game mail message reciprocating their feelings, stating that he also enjoys their company and likes it when they call him "Arn Peralun, Jedi Knight".