Well, from the title, one main character is likely the penguin. And since death is in the title too, death could be another main character, maybe personified as some kind of entity.
The main characters are usually the penguin avatars. There could be a brave little penguin who is always ready for an adventure, or a friendly penguin who loves to make new friends.
Since it's a graphic novel, the visuals would play a huge role. The art style could be used to depict death in a unique way, perhaps as a shadowy figure or a force of nature. The penguin, being the main character, might have its own personality. It could be a curious penguin that stumbles upon death's realm. Or it could be a penguin that is already marked for death and is trying to escape its fate, leading to an adventure full of challenges and self - discovery.
The main character is, of course, Death of the Endless. She is a central figure in the story.
Typically, the main characters would be those from 'The Death Cure' story. This might include Thomas, who is often at the center of the action, fighting against the virus and trying to save his friends. There could also be Newt, Minho, and other important characters who play significant roles in the battle against the Flare and the search for a solution.
Since I don't know the exact details of this graphic novel, Rorschach is likely to be one of the main characters, given the title. There might also be characters who are related to him, like his allies or enemies.
Since it's called 'The Merchant of Death Graphic Novel', the merchant of death is bound to be one of the main characters. There could be customers or clients of this merchant who also play important roles. Maybe there are some sort of enforcers or protectors in the story as well, who either help or hinder the merchant's activities.
There could be a doctor or a nurse as main characters. They would be involved in the care of the dying and might be facing moral and ethical challenges in their profession related to death. For instance, they may have to decide when to stop treatment or how to communicate bad news to the patient's family. Their stories can show the complex relationship between the medical field and death.
I don't know who the main characters are in the 'death of dulgath graphic novel' since I haven't read it.
In the 'Death of Daredevil Graphic Novel', Daredevil is the main focus. However, characters like Stick, who trained Daredevil, could be present. His presence might add some backstory to Daredevil's final moments. Also, the Punisher could potentially be a character in the story. Given his complex relationship with Daredevil, his reaction to Daredevil's death could be an interesting aspect of the plot.
It could be a group of survivors in a world filled with the living dead. There might be a strong - willed leader among them, a scientist trying to find a cure, and some regular people just trying to stay alive.