Deathstroke is from the 1980s and is a pretty amazing foe. He's often the nemesis of both Batman and the Green Arrow, so that could also be a hint of a new Justice League member.
If you've seen "Arrow" on the CW, then you know a little about Slade Wilson, who possesses enhanced physical powers and serious combat skills. And if you know comics, you know Marvel's "Deadpool" also began as a spoof of Deathstroke, aka Wade Wilson, who is played by Ryan Reynolds onscreen.
Here's the clip. Enjoy!
Here's the first "Justice League" trailer from last month's Comic-Con.