In comics, Prometheus saw his parents (who were criminals) gunned down by police. He vowed to destroy any kind of justice, found stolen money stashed away by his parents, traveled the world in order to train from terrorists and African mercenaries. He was part of Lex Luthor Injustice gang and was defeated by the Batman. He has a supercomputer attached to his body, Batman deactivated it, Martian Manhunter sent his mind on a psychological loop but was later killed, he escaped and went on a superhero killing spree. He had a part in Star city bombing which caused millions of deaths including Roy Harper’s daughter. Finally, Green arrow gets revenge on him by shooting him right through his head with an arrow.
On the show, he isn’t the same person from the Justice League comics, but he has the mindset as that of DC Villain. He is more like a version of Dark Archer from season 1 with a sword.His fighting style is impeccable with an amazing use of a wide array of weapons from bow & arrows to throwing stars, knives to axes. The mid-season finale of Arrow season 5 revealed the possible identity of the Prometheus, it’s been suggested that he is the son of a fallen pharmaceutical tycoon Justin Clayborn who was killed by “the Hood” as he failed the city by price gouging the essential medicine, rendering it unaffordable to thousands of families. Prometheus has destroyed Quentin Lance, severely hurt Curtis/Mister Terrific outside a party hall which led to his separation with his boyfriend, Oliver killed Billy Malone (boyfriend of Felicity) and Diggle is recaptured by the military.
Well, now we know that both Oliver & Prometheus were trained by the same woman Talia Al Ghul in Russia, Lexa Doig has already been cast for the role and will be seen in flashbacks. Her ties to League of Assassins is not a coincidence, and she may know the identity of Prometheus. The executive producer of the show Wendy Mericle has confirmed that Talia will play a critical role in demystifying the Prometheus identity.