I love my wizards. Gandalf, Merlin, Dumbledore. I love the gravitas, the familiarity, the tradition. But sometimes you need a witch. And not just any witch, but the most powerful, rugged old broad of a witch you can find, with the scars from the battles she's fought, a scowl that scares schoolchildren, and the depth of ability to go toe-to-toe with the Voldemorts of the world.
Minerva McGonagall was an ill-tempered crone, consumed with a fierce desire to do right, an obsessive sense of justice, and a mother's protectiveness of her students. Her intimidating presence often concealed her loving soul, and her ancient hidden heartache. Her own romance lost to the past, she poured her affection and commitment into Hogwarts and especially her Gryffindors. Woe to the dark witch or wizard who would threaten the school she lived for.
Always under Dumbledore's shadow, it was only late in her career that she stepped forth to assume stewardship of the resistance against Voldemort. Maybe she would never live up to the legends and myths of that famous wizard she had partnered with for so long. But there was a reason he had trusted her, and a reason her students respected and even feared her. This witch had game. And after a while you could see the wink in the arched eyebrow, the half-smile in the withered frown, and you knew that while this wasn't a woman to be trifled with, she was also more human than you had ever really considered. And when her time came, she was ready.