Can the main character and the antagonist be the same person in third person POV?
I'm writing a psychological thriller from a third person point of view (from the main character's view not the protagonist) My main characters objective is to find out who killed her husband and prove her innocence. However, I want her struggle to be more of a inner, emotional struggle rather than a guns blazing external struggle. I want the antagonist to be the inner demons of my main characters past that she needs to overcome in order to discover the truth. Is the main character able to also be the antagonist my main character needs to defeat? Or do they have to be two different characters? Answer:
Let's remember that stories are mental constructs in which different characters represent or symbolize different psychological drives.
It actually sounds like you want your main character to be the protagonist, in that she is pursuing the goal of identifying her husband's killer.
In that scenario, the antagonist would be the killer.
However, in some stories, the main character's inner conflict (or the subjective story) takes more of the spotlight than the external or overall plot. I think this is what you are concerned with here.
In the subjective story, there are two essential characters: the main character (MC) and the impact character (IC). The MC represents one approach to dealing with problems, the IC represents another. The MC's inner conflict concerns whether to stick with her approach or change and adopt the IC's approach.
Note: the MC in the subjective story can also be the protagonist of the external story. In that case, her inner conflict should be over the best approach to catching the killer.
For that matter, the IC can also be the antagonist --
for instance, if the demon from the main character's past turns out to be the killer.
However, let's say the IC is not the killer (because it's less predictable that way).
The IC could certainly be someone else from the MC's past. Memories of the IC could arise in the MC's mind during the course of her investigation, pressuring her to abandon her usual approach and try something different.
Or the IC could be an imaginary demon that comes to her in dreams, or a voice in her head that represents her subconscious or a suppressed part of her personality. You could also have various inner demons collectively function as the impact character, if they are all prodding her into abandoning her approach.
Sometimes the IC exerts pressure by telling the MC what approach she should take. Other times, the IC offers an example of how to take a different approach.
What matters is that the IC is a distinct entity that pressures the MC to doubt herself and consider changing.
What makes this more fun is that there is no way for the MC to know if adopting the IC's approach will help her catch the killer or be a fatal error. Her personal crisis is the moment when she decides whether to take the IC's advice and change or stick with her tried-and-true approach.
If you want her to "overcome" her demons, that suggests that she will ultimately be a steadfast character. She will reject the IC's approach and stick to her guns.
The reader then gets to see if that decision is right or wrong by whether the MC ends up better off as a result.
Hope that clarifies things. Best of luck.