Rourke, unfortunately, won't be one of the mercenaries. Instead, he's "an unscrupulous arms dealer who becomes the go-to guy" for the Expendables. Mix all that testosterone with Whitaker possibly playing a CIA liaison for the group, and Ben Kingsley circling the project, and you've got one heck of an unconventional action film -- UFC fighters*, action stars, has-beens, and praised actors. It also means that the dictator is screwed. I'm not sure any man could face these men (as a group) and live.
Now, if only Rourke didn't go and get that darned plastic surgery. He looked much tougher beforehand.
*Corrected thanks to Angry_Robot.