Minerva McGonagall. She was always tough but fair and always cared about Harry even though she didn't show it much. You see her true colors in the fifth book with Umbridge, and even more so in the seventh when Harry used an Unforgivable Curse because a Carrow spat at her, and when she cried out when she thought Harry was dead. I thought that touching to see how much they respected and cared for one another. Plus she's a total badass.