In "The Ransom of Red Chief", who are the main characters?

Sam (the narrator) and Bill are con-men passing through a small, rural Alabama town when they concoct a scheme to kidnap a child.  The kidnappers need money to finance a land fraud scheme they are planning to pull off later in Illinois.  Sam and Bill are the protagonists in the story.

The antagonist is the story is Johnny Dorsett, the only child of the town's most prominant citizen, and a terrible brat.  Johnny is kidnapped by the unsuspecting con-men to be held for ransom.

The entire premise of the story is ironic.  O. Henry was a master of irony and the ironic twist ending.  One would think the child, Johnny, would be the protagonist (usually the good guy) and the antagonists would be the kidnappers ( usually the bad guy), but the irony is that the kid turns out to be a giant pain-in-the-neck and the kidnappers can't wait to take him back.  The kidnappers are basically good guys who never intended to the harm the kid and actually take good care of him. 

Ebenezer Dorsett, the kidnapped child's father, is a minor character in the story.  He is a prominant citizen, a banker, and a church-going man so it is presumed that he would be anxious to pay the ransom for the return of his only son.  Of course, since the whole premise of the story is ironic, not only is Mr. Dorsett unwilling to pay the ransom, but in the end requires the kidnappers to pay him to take his child back.