Professor Lupin from Harry Potter by JK Rowling: I'm a sucker for a misunderstood young mentor figure, and Remus Lupin had total Mr. Keating vibes in the best way possible ("seize the day, wizards and witches")
Phineas from A Separate Peace by John Knowles: Even though of course we're supposed to love athletic, goofy, magnificent Finny because of how much Gene does, what I really loved about him was the quiet, well-meaning rebellion he practiced against the rules of his boarding school. Troublemakers are some of my favourite characters to read, which leads me to...
Alaska Young from Looking For Alaska by John Green: She made me snort with laughter, and then broke my heart. I suspect she did the same thing to Pudge.
Kel from A Darker Shade of Magic by VE Schwab: A cross between a mad magician, a brooding prince, and Doctor Who, I completely fell for this brilliant new hero and can't wait for the next book in the series.