After the decline of the Galactic Empire, a Human male Jedi student named Rosh Penin attended the Jedi Praxeum situated on Yavin 4, where he received instruction in the Force from Jedi Master Kyle Katarn.
Penin, along with other Jedi trainees, was en route to the Jedi Praxeum on Yavin 4 aboard a shuttle in 14 ABY. He encountered Jaden Korr on the ship, and they eventually formed a bond of friendship. The Disciples of Ragnos attacked their shuttle, causing it to crash-land. However, it was later revealed that the attack was a mere ruse to allow the cultists to gain access to Luke Skywalker's personal records stored in the Massassi temple.
Following their recovery from the shuttle crash, Penin and Korr joined forces to reach the temple. Within the rainforest, they battled aggressive howlers: Penin employed a blaster pistol for shooting while Korr wielded his lightsaber. After spotting stormtroopers guarding the Temple's perimeter, Korr proceeded alone, swiftly defeating them and a Sith Cultist. However, Tavion Axmis then struck him unconscious with the Scepter of Ragnos. Penin sought assistance, bringing Luke Skywalker and Kyle Katarn back with him, but the Disciples of Ragnos' forces had already departed.
Soon after, Katarn took on Penin and Korr as his apprentices, and their Jedi training commenced. During their inaugural training session, Rosh programmed a lightsaber training droid to target Jaden, intending to distract him and complete the training course ahead of him. While his scheme worked and Jaden lagged behind, Katarn rebuked Penin at the course's conclusion, asserting that the droid would have fatally wounded Korr had it been configured to Luke's training intensity. Penin offered an apology to his fellow student, which Korr accepted.
Penin frequently felt restricted by Katarn's instruction, leading to arrogance and impatience. Eventually, Penin was tasked with investigating Byss, where the Disciples of Ragnos captured him. Initially fearing for his life, he was instead exploited by them to embrace the dark side. The Cult easily swayed Penin due to his naiveté and hunger for power, making him an apprentice to Axmis, the leader of the Disciples of Ragnos.
On Vjun, Penin, alongside Axmis and the Kothos twins, directed the Cult's activities within Bast Castle to draw out the Force energies stored there. Katarn and Korr arrived on Vjun, seeking to thwart the cultists, but became separated. Korr eventually found and confronted Penin in Vader's throne room, where Penin, aided by the twins, engaged Korr in a duel.
The fight between Penin and Korr was closely contested until Korr eliminated the twins. Shortly after, he disarmed Penin just as Katarn arrived. Before they could capture Penin, Axmis intervened. She incapacitated Katarn and Korr with Force lightning, then revealed Penin as her new apprentice. Axmis used the Force to rip Korr's lightsaber from his grasp, threw it at the ceiling, and collapsed the weakened structure onto the Jedi using the Scepter of Ragnos. Amidst the ensuing chaos, she escaped with Penin. Katarn used the Force to prevent the ceiling from collapsing completely, while Korr utilized Katarn's lightsaber to create an escape route.
Later, while on Taspir III with Alora, Tavion's other apprentice, Penin regretted his actions and sought to abandon the dark side. He transmitted a distress signal to the Jedi Praxeum. Katarn and Korr arrived on Taspir III and began searching for Penin.
Korr eventually found Penin at an Imperial industrial facility, where Penin pleaded for forgiveness for his attack on Korr on Vjun, confessing that his fear had led him to the dark side. As Penin did not seem to need any help, Korr's anger at Penin resurfaced, and he nearly struck down his former friend. Katarn communicated with Korr through the Force, urging him to deactivate his lightsaber.
Korr complied, but Alora, who had been observing from afar, then attacked them. Alora's initial attacks included severing Penin's entire left arm as punishment for his betrayal, after which Korr defeated her in combat. Katarn arrived shortly thereafter, providing timely assistance as Penin went into shock, and his Master quickly transported him back to the Praxeum for medical attention.
While at the Praxeum, Penin tested his new prosthetic left arm, which was indistinguishable from his original arm. Luke Skywalker greeted him, expressing hope that Penin's experience with the dark side had instilled in him the patience and humility necessary to become a great Jedi. Penin gratefully accepted the Jedi Master's encouraging words.
Before his time at the Jedi Praxeum, Rosh Penin possessed great enthusiasm for becoming a Jedi. However, his training under Kyle Katarn led to arrogance and impatience. He developed the belief that Katarn was hindering his potential and failed to recognize his own capabilities.
For a period, Penin viewed his friend Jaden Korr as a competitor, striving to outperform him in their training. He succumbed to the dark side due to fear when confronted by the Disciples of Ragnos, embracing its power, but eventually acknowledged his error and returned to the light. He was readmitted to the Academy and took Luke Skywalker's advice on patience and humility to heart.
Rosh, despite generally being good-natured, had flaws such as overconfidence in his abilities and a tendency towards cowardice, as demonstrated by his easy persuasion to join a cult out of fear of harm.
As a Padawan, Penin demonstrated competence as a lightsaber duelist and mastered most of his fundamental skills, including Force protection, Force absorb, Force drain, and Force rage. He also displayed proficiency in using Force lightning and Force grip, employing both against Jaden Korr during their confrontation on Vjun following Penin's descent into the dark side.
Jason Marsden provided the voice for Rosh Penin in Star Wars: Jedi Knight: Jedi Academy. At the game's outset, Rosh wields a yellow-bladed training lightsaber. After his corruption by the dark side, Tavion Axmis gifted him a red-bladed lightsaber. An examination of the game's source files reveals that Rosh acquires a shadowtrooper's lightsaber, instead of one from a New Reborn. However, this has no effect on the lightsaber's appearance, as both types share the same hilt design.
During the fight against Rosh in Darth Vader's fortress, it is impossible to kill him because the two reborn accompanying him will restore his health if it gets too low. However, it is possible to sever his hand in combat. If this happens, Rosh will continue to attack as before, as his AI does not register that he no longer has his lightsaber.
The following information comes from the game's non-canonical ending.
After Jaden located Rosh on Taspir III, Jaden succumbed to his hatred and anger, deciding to kill Rosh. Rosh implored Jaden to release his anger before attacking him. Jaden disregarded his plea and impaled him with a lightsaber, inflicting a fatal wound. Jaden then killed Alora and fled to Korriban. Kyle arrived just as Rosh was dying and assured him that in returning to the light, he had become a true Jedi.