Back to that first principle of storytelling: A story is about someone who changes. And, puberty aside, Harry doesn't change much. As envisioned by Rowling, he walks the path of good so unwaveringly that his final victory over Voldemort feels, not just inevitable, but hollow.
But there is one character who does face a compelling inner crisis: Snape. With all the debate – and with all of Rowling's clues – about whether he was good or bad, it's fair to say that the sallow-faced potions professor has entranced many readers. His character ached for resolution.
And it is precisely this need for resolution – our desire to know the real Snape and to understand his choices – that makes him the most compelling character in the Potter epic. His decisions, not Harry's, were the linchpin. And his moment with Dumbledore after the death of Harry's parents, not Harry's last duel with Voldemort, is the authentic climax of the series.
For Harry, there was no choice. The way forward was clear, the conflict – and journey – external. We cared about Snape because this was not the nature of his story. Every action was weighted with the pain and subtext of his choices, or lack thereof. For Snape, there weren't – there couldn't be – any easy answers. And yet, in the end, his moral journey was overshadowed by this fact: It was merely one more plot device to propel Harry toward his pre-destined victory.
Snape: the authentic protagonist
Rowling has publicly expressed mystification over her readers' fascination with Snape, even suggesting that his appeal is simply "the bad boy syndrome." Instead, her readers, whether consciously or not, have tapped into something that Rowling herself may have failed to recognize.
That something was a need for a protagonist who genuinely struggled to define – and do – the right thing. A passive main character with no authentic moral dilemma is not only hard to relate to, he or she is also no guide in circumstances in which right and wrong...