Well, in a novel related to 'death's door', one might expect the main character to be someone on the brink of death. This character could be an old man reflecting on his life and the things he's done or left undone. There could also be a young character who has a near - death experience and has to come to terms with their own mortality at a very early age. And then there might be a character who has some sort of special ability or knowledge about death, like a shaman or a spiritual guide who helps the others understand what is happening as they approach death's door.
Since the title doesn't give much away about the characters, we can only guess. There might be a character who is in a desperate situation, like being at death's door. Maybe there's a guide or a foe associated with the Deadman's Cross. It could also be that there's a group of characters, some trying to survive and others causing trouble in this world that involves the Deadman's Cross.
I think the main theme of 'death's door novel' might be the transformation that occurs at the threshold of death. This could involve not just physical death, but also the death of ideas, relationships, or old ways of life. The novel may show how characters are forced to change when they are on the verge of losing something completely, and how this change can be both terrifying and liberating.
I'm afraid I can't say who the main characters are without more information about this 'a knock at the door novel'. However, it's common in such stories to have a protagonist who is affected by the knock at the door. There could also be the person or entity on the other side of the door. If it's a thriller, the main character might be a detective or an ordinary person caught up in a dangerous situation that starts with the knock.
Not having read the novel, I can only guess. There might be a brave explorer type of character who is drawn to the black door. There could also be a wise old mentor figure who tries to warn the protagonist about the perils of the black door. And perhaps there is an antagonist who wants to use the black door for their own evil purposes.
If it's based on the original 'A Wind in the Door', then Meg Murry is likely one of the main characters. She's a brave and intelligent girl. There may also be her brother Charles Wallace. He has special abilities and is an important part of the story. Another character could be Calvin O'Keefe, who is Meg's friend and helps her on her adventures in this strange world.
I don't know for sure since I haven't read it. But it could have a young protagonist who is curious about the wind in the door.
I'm not sure exactly who the main characters are without reading the novel. But it's likely to be the person who is considered the 'angel' and the one who notices this 'angel' quality, probably the neighbor or someone close to the so - called angel.
I don't know the main characters in 'lost door graphic novel' as I haven't read it. But they could be adventurers, like a brave young hero and his sidekick who are on a quest to find the lost door.
Since I haven't read the book, I can't say for sure who the main characters are. They could be anyone from an adventurous young person to an older, wiser figure.
Since I'm not acquainted with this novel, I can't name the main characters. You might want to check the book's description or other readers' comments.