Y'ull Acib was a male Human who operated as a member of the criminal organization known as Black Sun. Considered a dangerous criminal and among the most perilous individuals in the galaxy, Acib was incarcerated within the spice mines of Kessel. He was freed, along with sixteen others, by the New Republic on Coruscant with the intent of instigating disorder. Exceeding the Republic's expectations, Acib reestablished Black Sun on Coruscant, proclaimed himself Underlord, and governed the group briefly before being ousted by Durga the Hutt.
Y'ull Acib, a male Human, was a seasoned criminal who had been sentenced to imprisonment in the spice mines of Kessel by the Galactic Empire. While toiling in the mines, he encountered fellow prisoner Fliry Vorru. Both prisoners, in conjunction with fourteen others, were set free by the New Republic and dispatched to Coruscant following the capital planet's liberation from Imperial control.
The Republic's strategy, conceived by war hero Wedge Antilles, involved releasing the prisoners into Imperial City with the objective of creating chaos for any remaining Imperials who were either in hiding or attempting to maintain control over sections of the city. Although the plan was considered successful, the prisoners remained at large and dangerous long after the last Imperials were driven out. Collaborating closely with his ally Fliry Vorru, the last of the criminal Underlords, Acib embarked on a mission to restore the power of the notorious crime syndicate Black Sun.
Following the demise of Imperial Grand Admiral Thrawn, Acib successfully rallied the strength of the Undercity's most ruthless criminals, leading to the revival of Black Sun. Proclaiming himself Underlord, the leader of Black Sun, Acib ruled forcefully and rapidly accumulated increasing amounts of power. To prevent assassination or betrayal, Acib secluded himself in a secret location, rarely making personal appearances and conducting all meetings through hologram communication.
After the final death of Emperor Palpatine in 11 ABY, Acib forged an alliance with Grappa the Hutt in an attempt to seize control of the Imperial Interim Ruling Council. To achieve this, Acib orchestrated the successful assassinations of Councilmen General Immodet and Xandel Carivus. Prompted by Grappa, Acib planned to clone Carivus and replace him, deceiving the other council members. While assembling the clones on Ord Cantrell, the Imperials uncovered the deception and executed all of the clones. Upon discovering Black Sun's involvement, the Imperials directed their anger at Black Sun and initiated a hunt for Acib. In response, the Republic discovered the cloning facility, owned by Macus Kayniph, and destroyed it.
Deeming Grappa a failure, Acib's fears materialized when the Hutt was captured by Zanibar mercenaries and transported to Xo for a ritual sacrifice. After suffering such a significant setback, with the Imperials enraged and the New Republic in pursuit, Acib was easily overthrown in 12 ABY by Durga the Hutt. Claiming the title of Underlord for himself, Durga subsequently took control of the syndicate.