WARNING: The following contains spoilers for Justice League #65, on sale now from DC Comics.
Slade Wilson, the assassin known as Deathstroke, is one of the most fearsome adversaries in the DC Universe. Though most notably an arch-enemy of the Teen Titans, he's also famously taken out the entire Justice League at one point and was responsible for the loss of thousands of lives in the city of Blüdhaven. Now, however, it seems that the infamous Slade isn't the only person in the DC Universe calling themselves Deathstroke, as Justice League just revealed.
In the previous issue, Green Arrow and Black Canary had their romantic date interrupted when the former's Checkmate affairs showed up on their doorstep. In Justice League #65 by Brian Michael Bendis, Steve Pugh, Romulo Fajadro, Jr. and Josh Reed, things get even more complicated. After deciding that Checkmate's Daemon Rose was not their true enemy, the three were caught in an explosive attack by someone appearing to be Deathstroke.
Although they don't notice immediately, it isn't long before the two Justice Leaguers realize that the figure in front of them isn't their mortal enemy, but an imposter. The reason they notice this is because this Deathstroke didn't notice them. The mystery figure reveals that they only saw Arrow and Canary a split second before pulling the trigger that detonated the explosion. Slade would never be so reckless or unobservant and he definitely would have noticed if one of his biggest rivals was present.
Deathstroke and Green Arrow have been bitter enemies ever since the 2004 limited series Identity Crisis by Brad Meltzer and Rags Morales. In this series, Doctor Light hired the mercenary to defend him against the combined might of the Justice League. Slade was able to take each member of the team down one by one until Green Arrow brutally jammed an arrow into his empty eye socket. From that day forward, Deathstroke has made the emerald archer his main nemesis, even going to the lengths of infiltrating the League just to find a way to crash his and Canary's wedding.
This raises the question of who is now taking on the identity of Deathstroke. The most obvious suspects would be one of Slade's children, Joseph and Rose Wilson, otherwise known as former Teen Titans Jericho and Ravager, respectively. With Rose currently on Lazarus Island in Joshua Williamson and Gleb Melnikov's Robin series, it's unlikely to be her. The more likely Wilson kid would be Joseph, who hasn't been seen since the end of Christopher Priest and Carlo Pagulayan's Deathstroke series. However, considering how Joseph was growing more addicted to using his psychic powers in that series, it seems odd that he wouldn't use them here.
With Robin debuting a new Deathstroke-inspired character named Respawn, perhaps he could be the one under the mask. However, with that character taking part in the Lazarus Tournament alongside Rose Wilson, he probably wouldn't have the time to leave Lazarus Island to masquerade as his inspiration, although he could still be connected to what's really going on here.
The most likely explanation is that this imposter is a member of Deathstroke's shadowy new team, from his upcoming series Deathstroke Inc. by Joshua Williamson and Howard Porter. It could be that the unknown Respawn and this new Deathstroke are part of whatever Slade has gotten himself into, and taking out Checkmate here could be part of their overall goal. Considering Black Canary's animosity towards Oliver's involvement with that team, this could explain her joining Deathstroke in the upcoming series, as well as hint at her siding with this mystery assailant as the Justice League story unfolds.