Seff Hellin, a Jedi Knight, served the galaxy in the era after the Second Galactic Civil War. As a young student, he attended the Jedi Academy located on Yavin 4. During the war with the Yuuzhan Vong, he, along with the other students, was evacuated from the academy at the young age of fourteen. He was known for his curly hair.
Hellin was among the initial Jedi of the New Jedi Order to succumb to a Force-induced psychosis, which affected many across the galaxy around 43 ABY.
Around 12 ABY, Seff Hellin was born to a mother from Corellia. During the Yuuzhan Vong War, Seff Hellin and the other Jedi Younglings were evacuated to Shelter within the Maw. He was noted as the eldest of the group. It was at this time that Abeloth reached out to the younglings, planting the seeds of madness that would later manifest. The Jedi Masters remained unaware of this influence for years. He continued his training and became a Jedi.
By 43.5 ABY, he had achieved the rank of Jedi Knight.
Hellin played a crucial role in the rescue of Han Solo and his family when Allana was abducted on Taris. This involved the killing or injuring of several members of an arms syndicate operating out of Denon. Because he lacked the authorization to act on Taris, agents of Galactic Alliance Intelligence ordered Seff to surrender his lightsaber. Despite Leia Organa Solo's assurance that she would contact Jedi Grand Master Luke Skywalker on his behalf, Seff refused, claiming that Skywalker "didn't understand."
He then used the Force to disarm and temporarily paralyze the intelligence agents attempting to apprehend him, before fleeing the room with incredible speed. Leia commented that his abilities had surpassed what was normal. Consequently, Seff was declared a rogue Jedi, refusing to submit to the authority of the Masters by returning to Coruscant.
His actions on Taris further fueled distrust of the Jedi on the part of Chief of State Natasi Daala, leading her to deploy a team of Mandalorians to take him into custody. As a result, Luke Skywalker was compelled to recall all Jedi to the Temple on Coruscant until further notice, and to reassure Daala that the Jedi were capable of self-regulation and that Mandalorian involvement was unnecessary.
Seff harbored a deep mistrust of Daala's intentions toward the Jedi and the Mandalorians' involvement in Galactic Alliance affairs. Prior to the events on Taris, he approached Lando Calrissian without the authorization or knowledge of the New Jedi Order, regarding Tendrando Arms producing a Mandalorian Hunter Droid similar to the YVH class of droids.
Upon learning of Valin Horn's mental state, Seff became convinced that he and Valin were the only ones who had not been replaced by impostors. For weeks, Seff plotted to rescue Valin from the prison where he was being held in carbonite. During his rescue attempt, he was captured by a group of conspirators known as Darkmeld, led by Jaina Solo and Jagged Fel. Seff was sedated and secretly returned to the Asylum Block within the Jedi Temple, where Master Cilghal and Jedi Knight Tekli attempted to understand the nature of his mania.
When Chief Daala sought to take custody of all psychotic Jedi, the Solos smuggled them out of the Temple and transported them to the academy on Shedu Maad.
In 44 ABY, Hellin and the other Jedi afflicted by the mysterious Force psychosis regained their senses following Luke Skywalker's first battle with Abeloth on Abeloth's planet. Zekk and Tekli brought them from Shedu Maad back to the Jedi Temple. Hellin participated in the rescue of Jysella and Valin Horn as a member of "Team Saav'etu." Disguised as exterminators, the team employed foam coating to conceal the cam bubbles of the facility and then breached the outer walls using thermal detonators.
Inside, the team discovered thousands of prisoners frozen in carbonite alongside the Horn siblings. During the raid, Hellin secured the team's escape and successfully destroyed one of two Galactic Alliance Security troopsleds.