Yesterday, Volition announced that Agents of Mayhem will feature two exclusive heroes for those who have preordered the game; Johnny Gat and Lazarus. Lazarus is exclusive only if you preorder the digital edition of the game. It's confirmed that both agents will be sold as a separate DLCs at a later date post release.
Check out Gat's announcement trailer:
For more info on how to get Johnny Gat as a playable agent, check out this link: