Prometheus

A dark reflection of Batman, Prometheus was raised by criminal parents, who were gunned down by policemen right in front of him. Dedicating his life to destroying the law, Prometheus traveled the world and trained in the ways of murder. Clad in an armored suit that maximizes his natural skills, he is a master assassin whose physical and mental abilities rival Batman's own.

Before Arkham Origins Incident
It was around this time that Prometheus's parents were murdered by the police and he decided to become a criminal.

Arkham Origins Incident
It can be assumed he hadn't started his criminal life yet at this time, as he wasn't even considered to be hired by "Black Mask" to assassinate Batman. Seeing as he is an incredibly gifted assassin, this would be odd. Unless, of course, Prometheus wasn't for hire.

Between Arkham Origins and Arkham Asylum Incident
He'd definitely started his criminal life by this point. He had been apprehended by Batman at least once and was sent to Arkham Asylum, where he was treated by (presumably) Dr. Young, as she had taken personal notes on him.

Arkham Asylum Incident
It can be assumed he escaped the asylum before Joker's riot, as he was not encountered during the game. A newspaper clipping about him could be found in the Penitentiary.

Arkham City Incident
He didn't appear before Batman during the events of Arkham City. However, this could be because he hadn't been taken into the mega-prison. He was a great assassin, so it would be very difficult to apprehend him (especially when TYGER didn't have any help from Batman). If he had been incarcerated, however, he might have kept a low profile to avoid drawing attention (although this seems unlikely, given his profile).

Arkham Knight Incident
Prometheus made no appearance during the night of Halloween. This means he hadn't made an alliance with Scarecrow, Deathstroke, and the Arkham Knight. Possibly he had left Gotham City at the time, along with the other civilians.

Prometheus
Real Name: Unknown

Attributes

 * Pathological need to kill law officers
 * Trained to peak physical and mental levels
 * Arsenal of weapons and deadly gadgets
 * Hand To Hand Combat (Advance)
 * Firearms
 * Tactical Analysis
 * Genius level intellect

Trivia

 * Prometheus was one of the many villains to have a biography in Batman: Arkham Asylum and references in the other games, without making a physical appearance in the series.
 * He shares this trait with Killer Moth, Great White Shark and Ratcatcher, among others.
 * It could be considered odd that Prometheus had been incarcerated into Arkham Asylum, as he doesn't appear to have a serious mental illness (beside his tendency to kill all law enforcers he encounters), unlike the Joker, Poison Ivy or Scarecrow.
 * Prometheus was going to make his debut in the Arkham Knight DLC "The Season of Infamy", according to early in-game text files, but it was cut during development by Rocksteady. Black Mask was also cut from the "The Season of Infamy". Only Mad Hatter, Killer Croc, Mr. Freeze, and Ra's al Ghul appeared in the DLC, possibly because these villains had still-running story arcs, while Prometheus would be a new character, introduced in the last expansion of the last game of the series.