Nick Rostu was a male Korun, a member of the species, who participated in the Summertime War, the Clone Wars, and the Galactic Civil War. He was a nidôsh (an orphaned clan-child) belonging to the Ghôsh Rostu. Like all Korunnai, he possessed Force-sensitivity.
A significant portion of Rostu's early years were spent in Pelek Baw. This resulted in the loss of his original Korun accent and the attainment of fluency in Basic. Due to these experiences, he joined the Korunnai partisans during the Summertime War, gaining sufficient battlefield experience to be recruited into the Upland Liberation Front at the start of the Clone Wars.
Depa Billaba tasked Rostu with locating Jedi Master Mace Windu after Windu's arrival in Pelek Baw. Rostu, together with Lesh, Besh, and Chalk, rescued Windu from an ambush and escorted him into the jungle interior. They faced challenges such as militia gunship attacks and fever wasps before reaching Billaba's camp. Subsequently, Mace Windu appointed Rostu as his aide, a situation that would later cause frustration for both individuals.
Nick Rostu intended to leave Haruun Kal and become a mercenary. This was his primary motivation for accepting Mace Windu's offer, a fact he disclosed to Windu.
Rostu distinguished himself in the Battle of Pelek Baw and the Battle of Haruun Kal, operating heavy weapons and fighting with two slug-throwers. During the final battle, despite being seriously wounded by a vibroshield used by Iolu, he prevented Depa Billaba from committing suicide. Rostu was then transported back to Coruscant alongside Mace Windu. Although Windu only gave Rostu the rank of Brevet Major, a recommendation was submitted to the Galactic Senate to confirm it and nominate him for a Medal of Valor for his actions on Haruun Kal.
Throughout the war, Rostu served with the Grand Army of the Republic, commanding the 44th Division, which became known as Rostu's Renegades under his leadership. He saw combat on Ando, Bassadro, Atraken, and other battlegrounds. Rostu never forgot the fear, difficulties, and harsh conditions of each battle. He had anticipated a peaceful retirement after the Clone Wars. However, with the rise of the Galactic Empire, he was informed that he must pledge allegiance to the new government or face execution. Having learned about Mace Windu's fate earlier that day, Rostu refused, killed the officers, and fled into the Coruscant underworld, where he almost died on his first night at the hands of a street gang.
Six weeks later, Rostu saved the life of a wealthy Kitonak merchant. This merchant was a member of Whiplash, an underground resistance organization. Rostu was invited to join, and, despite the lack of pay, rest, and the high level of danger, he saw similarities between the movement and the Upland Liberation Front. With nowhere else to go and wanted for murder, he accepted the invitation.
While leading a group of resistance fighters, Rostu witnessed the death of Even Piell in an abandoned casino in Coruscant's Crimson Corridor, and promised to deliver his final mission to Jax Pavan.
After assisting Jax Pavan in escaping from stormtroopers in the Blackpit Slums, Rostu informed him that he needed to find a droid known as "Bug-Eyes," who supposedly held critical information for Whiplash. Later, back in the Zi-Kree Sector, he participated in a game of shronker, specifically Hot Bespin against a Yevetha. After defeating the Yevetha, he was captured by two smugglers and brought before Darth Vader.
After undergoing mental torture by Vader, he was instructed to bring Jax Pavan to him, or Vader would destroy Rostu's ghôsh on Haruun Kal. Feeling he had no alternative, he agreed. Ironically, it was Rostu's evident fear that prompted Haninum Tyk Rhinann to abandon Vader.
Rostu struggled with his decision, particularly when he reunited with Pavan, who was now working with the droid I-5YQ, the Sullustan reporter Den Dhur, and the Twi'lek Gray Paladin Laranth Tarak. He was eventually spared from having to make the decision. During an encounter with Black Sun members Xizor, Kaird, and Bug-Eyes in Coruscant's Factory District, Rostu was drawn in by Xizor's pheromones. When all his allies were captured, Rostu used the command code for Bug-Eyes to take control of the droid and attacked Xizor.
Xizor easily overcame him, and he was impaled by a piece of shrapnel, creating a slice in the opposite direction from his scar from Haruun Kal. During the ensuing duel between Pavan and Xizor, a reactor below the district was damaged. As Rostu felt he was dying, he explained his actions to Pavan and claimed he could see Mace Windu. Rostu, Pavan, and their allies escaped on the Far Ranger. After the damaged reactor exploded, Vader assumed Pavan was dead and ceased his pursuit.
During their escape, I-Five noticed that Rostu was still alive and stabilized him on the Far Ranger.
Some time after parting ways with Jax Pavan, Rostu met Aeona Cantor and began a relationship with her. Being Force-sensitive, Rostu attracted the attention of Imperial Agent Blackhole and was captured and taken to Mindor as part of Blackhole's plan to capture Luke Skywalker. This led Aeona to form a resistance movement on Mindor to rescue Rostu.
Under the control of Blackhole's Shadow Crown, a device that essentially made Rostu an extension of Blackhole's will, Rostu became his most powerful Pawn, known as Lord Shadowspawn—a title Skywalker later realized was a pun, referring to Rostu as "Shadow's Pawn" rather than "Spawn of Shadows." After being forced to engage in a staged battle against Skywalker, his meltmassif hat was accidentally damaged by Skywalker without triggering the fail-safe, which would have killed Rostu. This damage allowed Luke to free him from his enslavement, and he assisted the Jedi in rescuing Leia Organa and Han Solo, who had been captured by Blackhole using the body of Rostu's old enemy, Kar Vastor, when they arrived on Mindor to rescue Skywalker.
While working to rescue Organa, Rostu reunited with Cantor, and they commandeered Blackhole's personal shuttle to find the Imperial's true body. They returned to rescue Skywalker and Vastor, who were stranded when Mindor was destroyed as part of Blackhole's plan. Rostu then separated from Skywalker and, with Cantor and Vastor, continued to hunt down Blackhole, who had disappeared during his escape attempt.
Nick Rostu spent much of his youth in Pelek Baw, experiences that helped him become a competent officer in the ULF. Despite this, Kar Vastor often insulted him for actions that Mace Windu considered noble.
Rostu generally displayed a disrespectful attitude. He often used taunts and sarcasm and frequently questioned Windu's sanity. However, he could be a fierce fighter and a pleasant companion. The Summertime War was particularly difficult for him; Chalk, the woman he hoped to marry, was killed while he and Windu were trying to capture Kar Vastor.
Rostu initially admired Vastor. However, after spending time with Windu, he repeatedly expressed a desire (and even attempted) to shoot Vastor.
As a Korun, Nick Rostu had at least a minor connection to the Force. He was also a skilled shot with a blaster pistol, capable of shooting a lightsaber out of Depa Billaba's hand without harming her. On Mindor, he could shoot torpedoes from TIE bombers out of the sky, a feat that Luke Skywalker could only accomplish with the Force.