[quote=Foxxie]
It comes from Ancient Greek tragedies and drama (δευτεραγωνιστής), and it's used to describe the second most important character in a story. The deuteragonist can either be with or against the protagonist.
[/quote]

I see.

Thank you for explaining it to me.

So his character is important to the story and if you choose to be evil, you have to fight them.