The Hero
Summary: The hero is always the protagonist (though the protagonist is not always a hero). Traditionally speaking, the hero has been male, though fortunately there are more female heroes appearing in contemporary literature (think Katniss Everdeen and Lisbeth Salander). The hero is after some ultimate objective and must encounter and overcome obstacles along the way to achieving this goal. He or she is usually morally good, though that goodness will likely be challenged throughout the story. Heroes’ ability to stay true to themselves despite the trials they must face is what makes them heroic. That and the fact that they are often responsible for saving a bunch of people (or hobbits, or wizards, or what have you).
Examples of hero archetypes in literature: If you're a medieval literature buff, you'll be familiar with Sir Gawain of Sir Gawain and the Green Knight fame. If reading Middle English literature isn't your thing, here's a quick breakdown: Sir Gawain, after stepping up to the plate and taking on a challenge that none of the other knights were brave (or dumb) enough to take on, must go on an adventure that is almost certain to end in his death. He faces many challenges along the way—most important, there is a very tempting and very married lady that Sir Gawain must resist. The whole thing is a test of Sir Gawain's integrity and bravery, and—honorable knight that he is—he passes with only a minor indiscretion.
Though not everyone is familiar with Sir Gawain, I think it's fair to assume that most people have heard of Harry Potter. Harry represents the hero archetype almost perfectly. He takes on more responsibility than he should reasonably have to—teens aren't usually expected to keep the world safe from evil, after all—and remains brave even when he knows he faces certain death. Like many classic heroes, Harry conquers death, completes his mission, and never waivers from his true self, despite all the hardships he must face. Like many hero archetypes in literature before him, Harry is ethical almost to a fault. His friends accuse him of being a martyr, a role that often goes along with the hero territory.
The Mentor
Summary: The mentor is a common archetype in literature. The mentor is usually old, and this person often has some kind of magical abilities or a much greater breadth of knowledge than others possess. Mentors help heroes along their journeys, usually by teaching them how to help themselves (though mentors sometimes directly intervene in extreme situations). The mentor often ends up dying but is sometimes resurrected or revisited even after death.
Examples of mentor archetypes in literature: One word, folks: Gandalf. This infamous The Lord of the Rings wizard is the guy you want to have on your side when you're faced with an unexpected journey. He knows when to help; he knows when to back off. Gandalf's magical powers seem almost inseparable from his knowledge. He's definitely someone you want to have on your side when you're in a tough spot.
