[prōˈtagənist] : the main character in a novel, play, movie, etc.
To break down the definition of the word "protagonist" to middle school students, I explain that the protagonist is the "good guy" in the story and the antagonist is the "bad guy". Some synonyms include - hero, white knight, and champion. Of course, the more we read the more we know that it is never that simple. There are a few stories where our protagonist has flaws, but we still identify with and applaud him or her because they are basically "good". A student asked the other day who I thought was the protagonist in "The Crucible." I thought for a second, I would say John Proctor, what do you think? Though he was certainly not perfect [you know the whole adultery thing] in the end, he still wanted to protect his wife from the accusations of witchcraft.

To read more about these Protagonists or Antiheroes
Where Have All the Good Guys Gone?: On Game of Thrones, Mad Men, and Antihero Fatigue
Difficult Men: From The Sopranos and The Wire to Mad Men and
Breaking Bad by Brett Martin – review
The inside story of how the best TV series of the last 20 years came to
be made
FX's 'Tyrant' Drowns an Opportunity for Nuance in
Stereotypes by ERIC DEGGANS June 24, 2014
Mad, bad and dangerous to know: TV’s anti-heroes 17 JULY 2014
BAD MEN, MAD WOMEN APRIL 13, 2014 SUSANNAH SHARPLESS