Vax is an Enixian and one of the 218 prisoners who escaped from SAR TOP. Originally working for another Enixian, Kaiden, he is soon given a different task by Zin after Cole/Daggon takes Kaiden's life force.
It's unknown what Vax's crime was that led to his incarceration, but his dealings with fellow Enixian Kaiden may suggest he was into drug-dealing or was a bodyguard/assassin.
When Vax took over a human life-force, he was subordinate to Kaiden and helped him run a club that moved from place to place - which also sold the Enixian drug Feckmon to other prisoners as well as humans, before Zin ordered Kaiden to stop selling it to humans after one, a girl called Mandy, suffered a heart attack as a result. When Mel's friend Jess was at the police station giving details on Kaiden due to what had happened, an alien at the station informed Zin - who in turn informed Kaiden. Seeking to resolve the problem, Kaiden dispatched Vax to deal with Jess and Mel. Catching up to them after they left the Police station, Vax tried to kidnap both women. However, they were able to escape after Mel used her personal alarm - the high pitched sound causing great pain to Vax due to his senses being heightened. He later appeared at the club when Cole snuck in - watching as Cole's disguise wore off and revealed him to all the prisoners at the club. After Cole took Kaiden's life force, Vax and several other prisoners pursued him as he escaped with Mel, but were unable to capture him.
Some time later, Zin tasked Vax with finding and capture/kill Troy Montana (an actor who was the man in the underwear poster, whom Cole took the image of), after the previous criminal that Zin sent after Troy - an unnamed Nodulian in the body of a man called Adam Curtis - was killed by one of Zin's 'employees' for failing his task. With Troy framed for murder and Cole been wrongly arrested for it, Vax's task was to eliminate Troy so that Cole would be sent to prison and be out of the way. However, during his fight with Troy, Vax accidentally hit the fire alarm - with him becoming temporarily incapacitated and allowing Troy to escape. When Vax followed him outside, he could only watch as Mel (who had found out about Troy's return from Paris and had travelled to his apartment) convinced Troy to get in her car and drove off.
When Cole later escaped and managed to trade places with him and Troy using his hypertime ability, Cole headed for the parking lot area where Adam Curtis/the unnamed Nodulian had been killed - only to be confronted by Vax, who stated he should have killed Cole at the nightclub where Cole took Kaiden's life force. The two fight one another, with Cole outmatching and defeating Vax. When Cole asks for the tape (that was later altered to make it look like Cole had shot the Nodulian), Vax refused to say anything. Cole then smiled before pulling out his collector - telling Vax he could make the process quick and easy, or slow and painful.
Later in the courtroom, when a video is showing revealing the true culprit as Tanner (a woman on the jury), the woman tries to flee but is seemingly stopped by Vax. When she asks why he has betrayed them, he responds he is actually Cole in Vax's disguise - so it is certain he took Vax's life force.
Tracker (TV Series) - Episode 2: Cloud Nine
Tracker (TV Series) - Episode 10: Double Down