In honor of Harry Potter's birthday (the character, in-universe, was born July 31, 1980), it's easy to think of a hundred moments, lines, heartbreaks, and laughs that Harry and his pals have given us over the years. Since debuting in J.K. Rowling's Harry Potter and the Philosopher's Stone (retitled Sorcerer's Stone in U.S. printings) in 1997, Harry Potter has already given children of two generations (and those young-at-heart) inspiration as a hero for the ages.
But when did Harry really become a hero? Like many others, Harry Potter and the Prisoner of Azkaban, the third book and film, is a high point in the series to me. There's something extremely important that comes of Azkaban that in two books Harry had not dealt with at all: truly and directly addressing the post-traumatic stress that comes with being orphaned, prophesied, and championed. It's a lot for an 11- or 12-year-old to even contemplate, let alone understand, and it's not until he's 13 and has settled into his crazy wizarding life at Hogwarts that Harry begins to really process it all. In doing so, he also begins to become the hero the world expected him to be.
Now, Harry had absolutely done some heroic acts, largely at the assistance of Hermione and Ron, in his first two years at school. There's no question about that. But he couldn't truly transcend into a hero until he learned to save himself. In this story, he did so literally to learn how he could figuratively.
When Harry and Sirius are first saved from the Dementors at the lake toward the beginning of the third act, he thinks that somehow his father, James, has saved him from beyond the grave. In this, Harry looks to his still relatively new world of magic for a solution to an impossible problem. Remember that when the Dementors sucked away his happiness, they left Harry to dwell on his worst moment: losing his parents. Harry had never moved on from that moment, and did not trust himself to be able to. Instead, he clung to it, and his hope became his truth, as far as he believed it.
It's later that Harry, now traveling through time using the Time-Turner, realizes (just in time) that it wasn't his father standing across the lake (side-bar, coincidence or intention that the spell is Expecto Patronum and he was expecting his patron, traced back to the Latin for father?), it was his own self. Harry finally sees not just that there's something he has to do, and is capable of doing here, but also reconciles a bit that the only way his father (and by extension, his mother) lives on is through him. It's a truly breakthrough moment for the character, and the first time he moved beyond simply performing heroic acts to becoming a hero. By finding it within himself to save his own life, he also discovered the ability to truly save others.
From this point in Prisoner of Azkaban on through the end of the series, Harry takes on a new, much more active role. Whether it's leading the training in Dumbledore's Army, pro-actively joining the Order of the Phoenix, venturing forth to destroy Horcruxes, or even being willing to sacrifice himself to stop Voldemort, none of those moments or choices could have been made had he not first found the hero inside.
While Harry would have his moments of stumbles and setbacks, and like all suffering from PTSD would have other hurdles to leap on his road to recovery, his story of overcoming is one of the best lessons the Harry Potter novels ever taught.