The main difference between Deuteragonist and Protagonist is that the Deuteragonist is a the second most important character in a narrative work and Protagonist is a the main character of a creative work.
In literature, the deuteragonist or secondary main character (from Ancient Greek: δευτεραγωνιστής, deuteragōnistḗs, second actor) is the second most important character, after the protagonist and before the tritagonist. The deuteragonist may switch between supporting and opposing the protagonist, depending on the deuteragonist’s own conflict or plot.
A protagonist (from Ancient Greek πρωταγωνιστής (protagonistes), meaning ‘player of the first part, (chief actor)’ is the main character in any story, such as a literary work or drama.
The protagonist is at the center of the story, makes the key decisions, and experiences the consequences of those decisions. The protagonist affects the main characters’ circumstances as well, as they are often the primary actor propelling the story forward. If a story contains a subplot, or is a narrative made up of several stories, then the character who is interpreted as the protagonist of each subplot or individual story.
The word protagonist is used notably in stories and forms of literature and culture that contain stories, which would include dramas, novels, operas and films. In those forms the protagonist may simply be the leading actor, or the principal character in the story. More formally, the protagonist, while still defined as a leading character, may also be defined as the character whose fate is most closely followed by the reader or audience, and who is opposed by the antagonist. The antagonist will provide obstacles and complications and create conflict that test the protagonist, thus revealing the strengths and weaknesses of their character.
A person in a secondary role, specifically the second most important character (after the protagonist).
The main character, or one of the main characters, in any story, such as a literary work or drama.
A leading person in a contest; a principal performer.
An advocate or champion of a cause or course of action.