We know that Willem Dafoe is in Justice League, but that's about it. There's been a ton of speculation on the matter, so I checked in with my sources to see if they could offer any insight. They sort of, kind of did. What follows is like half a scoop.
According to my sources Willem Dafoe is playing an Atlantean. That's all I got for you. Start your speculation machines on which Atlantean he could be, although keep in mind that initial reports have him as a "good guy."
I do have some more insight into how they'll accomplish Atlantean stuff in Justice League (and, I assume, Aquaman, which went back to the drawing board in the last week or so with a complete page one rewrite). In Batman v Superman: Dawn of Justice Aquaman's cameo was marred by the fact that Jason Momoa was very, very clearly holding his breath in a water tank. Like, his cheeks are all puffy as if he were chilling on the bottom of the pool at his parents' house. It's not a good look for an amphibuous hero. My sources tell me that rather than shoot in a water tank this time Zack Snyder has set up an elaborate rig on a green screen stage - it's a two armed rig, with Momoa clutched in one arm while the camera is clutched in the other. They two arms are preprogrammed to move in sync so that Momoa can do all kinds of maneuvers while the camera moves around him. I'm assuming there's a similar rig for more elaborate flying stuff. Momoa's hair will be CGIed into a flowy, underwater look.
That isn't the only greenscreen on the film. I'm being told that a majority of the movie will be shot on sets and Snyder will utilize background replacement, similar to his approach to 300. This offers him more control on the visuals of the film, but it also keeps the costumed characters away from prying cameras.
OK, it's in your court - is there a 'name' Atlantean you could see Dafoe playing? Speculate away.