In literary work, the main character is known as, while the opposing is known as

The main character is the protagonist while the opposing is the antagonist.

The main character is known as the protagonist, while the opposing character is known as the antagonist. Side note, protagonist and hero aren't synonymous. Your main character could be a villain, morally gray, etc. Antagonists aren't always evil. Sometimes it's the fact that they're opposing what the protagonist wants to do, which could be good or bad.