Hercules final labor was to capture Cerberus, the three headed dog that guarded the underworld. Hercules got permission to take Cerberus from Hades, but Hades told him he could only have him if Hercules subdued him without using any weapons.
Batman Art - "Because he's the hero that Gotham deserves, but not the one it needs right now. and so we'll hunt him. because he's not a hero. he's a silent guardian, a watchful protector. a Dark Knight.