I'm not sure who the main characters are specifically. But since it's about the Atom in a punk setting, the Atom himself is likely a main character. There might also be some original characters created for this version of the story that interact with the Atom, like a punk - inspired sidekick or an anti - hero who teams up with the Atom.
Since it's a 'dc comics atom punk graphic novel', the Atom is bound to be one of the main characters. However, in a punk - inspired story, there could be a whole cast of interesting characters. There might be a street - smart informant who gives the Atom crucial information. There could also be a group of rebels who the Atom either joins or has to fight against. And perhaps there's a mad scientist - type character who is responsible for some of the chaos in the Atom's world, creating new challenges for him to overcome.
The Atom is surely a main character in the 'dc comics atom punk graphic novel'. He's the central figure in Atom - related stories in DC Comics. In a punk - themed story, there could be other characters that are products of this unique setting. For example, there might be a punk - rocker type character who has some special knowledge or ability that helps the Atom in his journey. There could also be a villain who represents the corrupt or oppressive elements of this punk - inspired world.