Who is considered to be the nemesis in the story?

A nemesis is your protagonist’s foremost enemy. He or she diametrically opposes everything your main character values or believes in. Think arch-villain, arch-enemy, or arch-foe.
 

Are nemesis and antagonist the same thing?

Antagonists are defined as characters that work in opposition to the protagonist (the hero). Villains are defined as “evil” characters intent on harming others. A Nemesis is defined as a long-standing rival; an archenemy.
 

Does the antagonist have to be a person?

An antagonist doesn’t have to be human—the main antagonist can sometimes be a force, like nature. A good example of this is the sea in Robinson Crusoe.