Nanny McPhee (small c, big P), is the main protagonist in the Nanny McPhee films. She was portrayed by Emma Thompson.
She is an immortal witch and nanny and her job is to discpline bad children and make them be good children. In the end of the movies she turns from ugly to beautiful.
Her work is "When you need me, but don't want me, then I'll stay. But when you want me, but no longer need me, then I'll have to go."
Gallery
Nanny McPhee's initial appearance
Nanny McPhee's true appearance