A red-headed person, so called on the assumption that a person who has red hair above must also have red hair below. See also muff.
Envious damsels cruelly love: / They called Gemima 'Copper Muff' / And 'Orange Juice' and 'Gingerbread'. / She never heeded what they said, /But, silent, combed her glist'ring curls /And shunned the spiteful jealous girls.
Alfred, Lord Tennyson - from 'Ginger Gemima' (1854)