There are a lot of things to celebrate about the Harry Potter books, many of which I've touched on earlier in this list. One of the things I cherish most about the series is the realistic depiction of teachers. Rowling deftly avoids the pitfalls that commonly afflict fictional handling of schoolteachers. They're often shown as unforgiving martinets or backslapping doormats, with little nuance in between. The staff at Hogwarts are drawn with much greater humanity and diversity, as is true in real schools. Some teachers are boring, some tough, some friendly, some incompetent, some brilliant. Some teachers even manage to be all of those things on different days.
Of the teachers at Hogwarts, my favorite was Remus Lupin. I like Lupin for a lot of reasons - I like his shambling, exhausted demeanor, his tattered optimism despite his lycanthropy, his willingness to listen, his fierce loyalty, his commitment to defeat Voldemort - but what really shines through to me is what a fantastic teacher he is. He clearly knows his material, and he consistently finds fresh and innovative ways to engage his students. Learning is fun in his classroom, and he is always patient and friendly with his students, but he is not a pushover. He's clearly in charge, though not a tyrant. Harder to do well than those who have never managed young learners might imagine.
Lupin had to die, of course - he was the last link to Harry's father, and Rowling seemed set on clearing out that entire cohort. At least he found some joy at last with Tonks. He left behind a son he would never know, just as his friend James Potter did. And where Lupin joined the ranks of surrogate fathers for Harry, Harry himself was able to return that love with orphaned Teddy. That entire brief arc was an understated, well-crafted coda to the series, giving Harry the chance to pay back (or forward, or whatever) some of the kindness he received.