Oliver's Son

This is a theory we've previously touched on in our Fan Fridays segment, and it's still not entirely impossible.

It has been said time and time again that Prometheus is truly a "creation" of Oliver, and there's a very chance that could be taken literally. While Oliver obviously already has one illegitimate son, as was covered in Season 4, William is far too young to fit the bill. And while Connor Hawke - previously seen taking up the Green Arrow mantle in an alternate future timeline on last season of Legends of Tomorrow - is Oliver's son in the comics, he was changed to be the son of John Diggle.

But there is a very small chance that Prometheus could be Oliver's son from the future. With the Legends currently hopping through time and The Flash causing some changes of their own this season with Flashpoint, Prometheus could be a product of either of those things.

However, this doesn't explain the current situation with Prometheus' parents, with Oliver tracking down the villain's mother in tonight's episode. But stranger things have certainly happened on these shows, making this a still plausible - but highly unlikely - theory.

Roy Harper

This theory was suggested as early as November of last year, and we covered it in our Fan Fridays segment as well.

The theory is that Oliver's protégé, Roy Harper, could actually be behind Prometheus' mask.

Roy has only been seen sparingly since his departure from the show in season three (after Colton Haynes left the show due to personal issues). Haynes went on to appear in the second season of Fox's Scream Queens, which finished airing in December, making his schedule clear to return to Arrow.

While Roy's past alliance with Team Arrow and his seemingly happy exit from the team, both in season three and season four, it initially seems unlikely that Roy would be the maniacal villain. But, as we discussed when we initially presented this theory, Roy's return could also incorporate elements from one of Arrow's sister shows.

As was seen throughout the first part of The Flash's third season, the creation of the Flashpoint timeline, and the subsequent changes to the timeline that resulted when Barry tried to reset things, had effects on previously innocent citizens of Central City. Many of the villains Team Flash faced in those episodes were people who had powers or evil identities in the Flashpoint timeline, which were now being reflected in their present selves.

So could this have happened to Roy? It certainly would be an interesting twist, and one that would not only include the show's theme of 'legacy' - given Oliver's past mentoring of Roy - but would bring Roy's past love interest, Thea, further back into the ongoings of Team Arrow.