A new casting notice out for an as-yet-unannounced episode of Arrow seems to have announced the first appearance of a new vigilante in the series.
Spoiler TV is saying that "Episode 1.18 will see a character called 'The Savior.' He is also a vigilante who dishes out death sentences on the Internet."
There's no DC superhero or villain who fits that description, although there was a Superman villain for a time in the '90s who went by the name "Savior." He believed that God was talking to him and that it was his job to kill "deceivers," such as corrupt politicians and religious figures. That group also at the time included Superman who had recently returned from the dead (Savior thought he was an impostor).
It's a very long shot, but worth mentioning. He would probably see himself as a vigilante, and a Arrow/real-world version would likely be a guy with no powers doing his thing in whatever way he saw fit.