WARNING: The following contains spoilers for Justice League #64, by Brian Michael Bendis, Steve Pugh, Nick Filardi and Josh Reed, and for Checkmate #1 by Brian Michael Bendis, Alex Maleev and Dave Stewart, on sale now.
Green Arrow is a member of the Justice League, but after he also joined the newly-reformed organization Checkmate, the Emerald Archer soon found himself in the cross hairs of a mysterious sniper known as the Daemon Rose. And Oliver Queen is not the only person that this sharpshooter seems to be gunning for.
The sniper has also set his eye on Lois Lane, another of the people working to rebuild Checkmate, and he was quite literally scoping her out through his rifle. The Daemon Rose's true identity is a mystery, but there have been some clues that suggest who he might be.
After the secret organization Leviathan absorbed most of the technology and resources of the various agencies that monitored superhuman activity, a group of the world's greatest detectives came together to respond to the threat that Leviathan posed. Included in the investigative team were Green Arrow, Lois Lane, Talia al Ghul, and the occult investigator John Constantine. They reformed Checkmate, formerly a US- and UN-backed government organization that policed the activities of metahumans.
At the conclusion of Checkmate #1, Lois Lane received a mysterious parcel from Leviathan. The issue ended with her looking out her office window at the Daily Planet, unaware that she was in the Daemon Rose's sniper sites. The last panel showed his face shrouded in shadows. From this, it's clear that he is not part of Leviathan. After all, he was not involved in delivering the package, and if Leviathan wanted to kill or spy on her, their superior technology gives them much better options than a rifle.
His appearance in Justice League #64 revealed a bit more. In this issue, he stalked Green Arrow and Black Canary while they were enjoying a romantic outing. The Daemon Rose's goal seemed to be surveillance rather than assassination, as he intentionally passed up at least ten clean shots, according to Green Arrow. The two Justice League heroes managed to disarm and apprehend the assassin. When they asked who he was, he said that they would be familiar with him as the Daemon Rose--a title neither hero had heard before. He also alluded to an interest in Green Arrow's affiliation with Checkmate. This suggests he has ties to another organization with its own agenda, one that has an interest in Checkmate's return. Also, being called "the" Daemon Rose suggests this is a professional title or nickname.
In an interview with Newsarama, Bendis said that the Daemon Rose "has a very, very deep connection to the Superman universe." That might not seem to narrow it down, but when added to the other clues, it suggests that the sniper might have worked for an older incarnation of Checkmate. In the events leading up to Infinite Crisis, Superman was being mind-controlled by the head of Checkmate, Maxwell Lord. This (and the group's use of unethical technology) led to the organization being dismantled. A former Checkmate agent might want to keep tabs on anyone trying to reform the agency. Alternatively, he could have worked for another agency that has since been absorbed into Leviathan, possibly even serving under Lois's father, the late General Sam Lane.
Another possibility is hinted at in the name. Daemon is the homeworld of the alien Daemonites, who are capable of shapeshifting. The Daemonites were originally part of the WildStorm Universe but were later incorporated into DC continuity. Superman has fought against Daemonites such as the murderous warlord Helspont. Alternatively, he could just as easily be from one of the many other humanoid-looking alien species that Superman has encountered, although most of these race are so powerful that they would have no reason to use a sniper rifle to eliminate a target. Whatever the case, the Daemon Rose is part of an intriguing mystery that is just beginning.