I just picked up Event Leviathan issues 1 and 2 today, and I regret not picking them up sooner. I have a couple of theories on who Leviathan could be, and I’m sure I’m not the only one. Feel free to post your theories here.
Personally, I think it’s either Roy Harper or Damian Wayne, but most likely Damian.
Roy would make sense because he’s got the motivations after his “death” in Heroes In Crisis, as well as serving as a meaningful connection to both Red Hood and Green Arrow.
Damian Wayne makes even more sense to me. He had a past with Talia al Ghul and Leviathan, he has the training, he could definitely build a Batman-style mask like the one the Leviathan agent used, and he was pretty quick to make Jason his prime suspect.