“Arrow” has a big mystery to solve: who is the new villain? Prometheus still hasn’t faced Oliver, but it’s clear that the new nemesis has a massive problem with the emerald archer. The CW drama hasn’t reveal the character or actor behind the mask. That seems to indicate that audiences will recognize the big bad when he takes the mask off. Naturally, we have a few theories about who it could be.

While there isn’t much evidence at this point, showrunner Wendy Mericle previously said that Prometheus has a connection to Season 1. “[The villain] is somebody Oliver unwittingly created in Season 1 when he was a killer in a hood,” Mericle said in a print edition of TV Guide in July. “This guy is going to be collateral damage who lost someone to the Hood and [has] spent the last several years training and plotting for revenge. He will be a true dark mirror to Oliver Queen.”

Oliver (Stephen Amell) wasn’t too picky about who he killed back in his Hood days, so that still leaves a pretty extensive list. Still, it seems likely that the masked villain will be someone of importance.

Tommy Merlyn — This seems to be the most popular fan theory. Tommy (Colin Donnell) definitely died in Season 1, but Flashpoint could have changed anything. If Tommy is alive, there are plenty of reasons to be angry with Oliver. He could blame his death, his father Malcolm’s (John Barrowman) role in the League of Assassins and Laurel’s (Katie Cassidy) death on the Green Arrow.

The problem here is that Colin Donnell has a regular role on “Chicago Med,” which films in the Windy City while “Arrow” shoots in Vancouver. However, that might be why Prometheus is staying hidden for so long. Donnell doesn’t actually have to be there until the mask comes off later this season.

Slade Wilson — We know Deathstroke (Manu Bennett) is coming back, but maybe he’ll return before the 100th episode. He may have adopted a new look to avoid tipping anyone off, and fans know that he has plenty of issues with Oliver to justify killing him.

Billy Malone — Let’s face it, something is probably wrong with Felicity’s (Emily Bett Rickards) new boyfriend (Tyler Ritter). Billy seems a little too squeaky clean. Yes, he tipped off the Green Arrow, but maybe that was a ruse to keep his identity concealed. As for the Season 1 connection, perhaps Oliver killed someone close to Billy a few years ago. Ollie didn’t have the best relationship with the cops at the beginning of his vigilante career. Perhaps one of Billy’s buddies or family members were killed by the Green Arrow.

A Vigilante — Could Wild Dog (Rick Gonzalez) or one of the others actually be working against Oliver? They’ve all clearly been affected by the vigilantism in Star City. Perhaps they don’t all admire the Green Arrow as much as we think. We don’t know much about all of their families, so any one of them could have suffered a tragic loss that is connected to their mentor.

“Arrow” Season 5 airs Wednesdays at 8 p.m. EDT on The CW. Who do you think is going to be Prometheus? Sound off in the comments section below!