Sull was an Alpha-class ARC trooper in the Grand Army of the Republic. He was one of the several ARCs that was cloned and trained by bounty hunter Jango Fett. Sull was deployed to the planet Gaftikar. When he reached the planet, soon after training the creatures known as Marits, failed to report in to command. The Special Operations Brigade sent in the clone commando squad Omega and Null-class ARC A'den to investigate.
They discovered Sull, who had been living in an apartment for the weeks he was "missing". Omega took him back to A'den for an interrogation. The two discussed some terms and A'den called his Nyreen "Ny" Vollen to take Sull off planet, despite Niner's, the sergeant of Omega, interjections. Sull would explain that he tried to escape after what happened to his friend Tavo, who had been caught by Covert operations troopers and executed him. After Sull left Gaftikar, Omega's weapons specialist, Darman, was sent to clear out Sull's apartment. He was met there by two covert ops troopers by the names of Moz and Olun, whom he killed.
Ny would drop Sull at the planet of Mandalore, where he would meet Alpha-02, or Spar who he develop a friendship with. They would meet Fi, a former member of Omega, who had been blown up and had brain damage. The three would meet Fenn Shysa, who tried to convince them to become Mand'alor, the leader of the Mandalorians. Sull and Fi declined, but Spar accepted.
Sull, Spar and Fi would all go to Coruscant to help Kal Skirata and his clan escape the GAR. The three assisted in retrieving several prisoners from Republic prison. After retrieving them, Sull and Spar would go back to Mandalore with Jilka Zan Zentis, Ovolot Qail Uthan, Ruusaan Skirata and another Null named Mereel. Afterwards, they remained there until the rest of Clan Skirata returned. However, Jedi General Etain Tur-Mukan was killed and Niner was injured, which forced Darman to stay on Coruscant with him.
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