First thing first: as he promised yesterday, Johnson gave his fans the link to the Hercules trailer on Twitter. In the sneak peek, Hercules starts chained up (for killing his children and wife when driven mad by Hera) before breaking out and starting the "twelve labors of Hercules."
There's a glimpse of several of his labors, including his battles against the Lernaean Hydra, Nemean Lion, and Erymanthian Boar. Johnson bellows only one line in the entire trailer: "I am Hercules!"
However, that's not all. Johnson also revealed he has agreed on a character to portray in a DC Domics film. He wrote on Twitter, "Myself & DC have agreed on a character.. extremely complex, well known (but never played) and a pure BAD ASS MF;) #RockTalk." He also dashed hopes he'd play Green Lantern John Stewart, explaining Green Lantern has "already been played."
Who does that leave? Well, as a comic book aficionado, my best guess would be Cyborg (below). The character went through a spike in popularity thanks to the animated Teen Titans and is also one of the main members of the Justice League, which is the superhero group DC and Warner Bros. are trying to put together.