I'm not entirely sure without reading the book specifically, but it could be soldiers or leaders in a military - type setting, given the title's connotations of a fight to the end.
The main theme could be about heroism and the lengths people will go to in the face of extreme challenges. It might also touch on loyalty and sacrifice as the title 'To the Last Man' implies a sense of giving everything until there's no one left.
I don't know for sure since I haven't read the novel, but typically in a Shaara novel, there might be strong - willed individuals who are faced with the challenges presented by the 'rising tide' concept.
Since I'm not familiar with this novel, it's hard to say exactly. But if it's like other Shaara novels, it might have leaders on different sides of a conflict as main characters. They could be military leaders with strong personalities and different ideologies, or ordinary people who find themselves in extraordinary circumstances and become central to the story.
Often in such novels, there are supporting characters. These could be friends or family members of the main character. They might not have as much power or influence as the lead, but they contribute to the story in their own ways, like providing emotional support or helping with practical tasks.
The main character is the 'last angry man' himself. Around him, there could be family members such as a wife or children who either support or are at odds with his angry nature. There may be neighbors who are affected by his actions or words. And perhaps there are colleagues or people from his workplace if the story has that aspect. There could also be a local community figure, like a priest or a community leader, who tries to mediate or influence the angry man's situation.
I'm not sure specifically as I haven't read this particular 'To the Last Man' by Grey Novel. But typically in such a story, there could be a strong, determined male lead who is the one likely to be the last man. There might also be a female character who provides support or motivation to the male lead.
It's possible that there is a character who is a scientist like Frankenstein. This character could be either trying to correct the mistakes of Frankenstein or repeating his same errors in the context of a world that is on the verge of extinction. And then there could be a female character who serves as a moral compass or a source of hope for the last man.
Well, obviously, there's the last man in the tower. But there may also be other characters who are either in his memories or have some connection to the tower even if they are not physically present in it. For example, there could be people he used to know before he became the last man there.
Most likely Spider - Man himself. And perhaps his love interest, like Mary Jane. Also, his friends like Ned could be there.
Since the title is so unclear, it's impossible to say who the main characters are. It could be that the 'last man' is the main character, but without more context, we can't be certain.