Tam Posla was a Milvaynian human male from the planet Milvayne. He became a respected lawman in the law enforcement known as the Milvayne Authority and eventually began investigating a rash of crimes by the criminal surgeon Cornelius Evazan and his partner Ponda Baba. Although he was taken off the case, he went rogue to continue pursuing the pair, becoming a bounty hunter and vigilante when his superior officer had him discharged.
Unable to apprehend Evazan and Baba on the moon Jedha, Posla found and fell in love with one of their cyborg prototypes, Caysin Bog, and the pair continued the hunt together. To gather funds for their hunt, they took a job in which they joined a crew of mercenaries led by the rogue archaeologist Chelli Aphra. The crew undertook a series of missions, going on to infiltrate the Imperial base Hivebase-1.
At Hivebase-1, Aphra catalyzed the death of Bog at the hands of attackers in order to make Posla fight them. Once their mission was complete, she conspired with the Imperial Magna Tolvan, who stole the vigilante's attire and left him gagged while she stowed away with the rogue archaeologist. Posla suspected Aphra of being responsible for Bog's death but continued his hunt for Evazan, tracking the rogue surgeon's history up until a dead end.
Aphra then asked Posla to help her escape the Imperial wreckage-prison Accresker Jail in exchange for a captive Evazan. The vigilante agreed to a trade and brought an escape shuttle to her at Accresker, taking away Evazan frozen in an ice chunk. However, when being freed from the ice, Evazan used a shape-shifting creature to pretend to be someone else, tricking Posla into thinking he had been deceived. The vigilante returned to Accresker Jail and confronted Aphra, only to be attacked and killed by the assassin droid 0-0-0.
After his death, Posla's corpse was found and merged into by some Force-sensitive Gundravian hookspores, reviving the vigilante and giving him Force powers. The undead Posla tracked down and pursued Aphra and 0-0-0 on Milvayne, losing them multiple times. When the vigilante later joined an Imperial garrison attacking the pair, he was set on fire by 0-0-0. Before burning up, he fired a shot that triggered a series of events involving mass rioting on Milvayne.