20 Big Questions About 2017's Most Hotly Anticipated TV Shows

20. Who Is Prometheus? - Arrow

Prometheus is the mysterious villain stalking the streets of Star City, intent on getting revenge on Oliver Queen. The masked archer was 'created' by Ollie, a direct result of his actions way back in Season 1, and has spent the time since honing his skills in order to take him down.

He apparently has some connection to Artemis too, after she decided to join his side in the fight against Team Arrow, but the character is still mostly shrouded in mystery.

Theories range from Tommy Merlyn to Helena Bertinelli aka Huntress, or perhaps Yao Fei. It has to be a face we/Oliver would recognise, because otherwise there's little point in building up such a mystery, but as yet there's nothing concrete to go on - and there likely won't be until we enter the final third of the much-improved fifth season.