Since I haven't read the novel, I can't say for sure. But I would expect the undead king to be a main character. There might also be some loyal followers or advisors to the king, perhaps a wizard or a brave knight who has pledged their service to him.
The plot could revolve around the undead king facing various challenges while trying to maintain his reign of peace. There might be other powerful entities that oppose him, and he has to use his undead - related abilities, like controlling the undead army or having some sort of immortality - based wisdom, to deal with political intrigue, battles, and social unrest in the land he rules.
The obvious main character would be the undead king himself. He is likely to be at the center of the story. There could be other important characters such as his advisers, if he has any. They might be undead as well or some other dark entities. And there may be characters from outside the palace who try to enter the palace of darkness for various reasons, like treasure hunters or adventurers, and they could also be main characters as their actions might drive the plot forward.
Obviously, the undead king is one of the main characters. He is central to the story as the title suggests.
Harry Potter would surely be one of the main characters as it's in his name. And his friends like Hermione and Ron might also be important. Since it's about the king of the undead, there could be some new characters introduced who are undead themselves, like a vampire wizard or a zombie witch that either help or oppose Harry in his new role.
I'm sorry, I don't know the specific main characters as I haven't read the novel.
The main characters include the different claimants to the Superman identity. There was the Cyborg Superman, who had a mechanical body. Then there was Superboy, a younger and more brash character. And of course, the Eradicator, who had his own set of powers and motives. There was also Steel, who was more of a technological hero in his own right.
Since it's about the seven spellblades, there could be a group of characters. Maybe a brave knight who is tasked with protecting the spellblades from falling into the wrong hands. There might also be a wise old mage who has knowledge about the spellblades' origins and guides the younger characters. Another possibility is a cunning thief who is initially after the spellblades for personal gain but then gets involved in a bigger cause.
The undead king himself is very interesting. His power and his unique perspective as an undead ruler make him stand out. Also, some of his loyal minions like Albedo are quite fascinating. Her unwavering loyalty and her complex personality add depth to the story.
I'm not sure who the main characters are without more information about the 'Dark Reign Story'. It could be a villainous ruler and the rebels who oppose them.
Since I don't know the 'disturbing the peace novel' in question, I can't say for sure. But usually, there would be characters who are the instigators of the disturbance and those who are affected by it.