Short answers, pulled from the story.
A protagonist is the main character of a story who makes key decisions that affect the plot and faces the most significant obstacles and choices. The protagonist's fate is most closely followed by the reader or audience, and the character is opposed by an antagonist whose conflicts reveal the protagonist's strengths and weaknesses.
The word protagonist comes from ancient Greek, combining a root meaning "first" with a term meaning "actor" or "competitor," which traces back to a phrase meaning "I contend for a prize." The term emerged from ancient Greek dramatic tradition, where the protagonist was the primary actor on stage.
According to Aristotle's Poetics, a poet named Thespis introduced the idea of one actor stepping out from the chorus to engage in dialogue with it around 536 BCE. This act is credited with inventing tragedy. The poet Aeschylus later introduced a second actor, and Sophocles added a third.
A protagonist is the main character of a story, defined by narrative centrality, while a hero is a judgment about character, typically admired for strength, courage, virtuousness, and honor. A protagonist can be a villain, an antihero, or a morally compromised character. In ancient Greece, hero specifically referred to a human who had become a semi-divine being in the narrative.
A villain protagonist is a main character who is a villain, driving the story forward despite cruel, malicious, or wicked qualities. Examples include Tony Soprano from The Sopranos, Walter White from Breaking Bad, Humbert Humbert in Vladimir Nabokov's Lolita, Frank Underwood in House of Cards, Light Yagami in the Death Note franchise, and Richard III in Shakespeare's eponymous play.
A false protagonist is a character who appears to be the protagonist but then disappears unexpectedly. The character Marion in Alfred Hitchcock's film Psycho (1960) is the most cited example, appearing to be the central figure before vanishing partway through the story.