late 14c., protectour, "a defender, guardian, one who defends or shields from injury or evil," from Old French protector (14c., Modern French protecteur) and directly from Late Latin protector, agent noun from protegere (see protection). Related: Protectoral; protectorial; protectorian. Fem. forms protectrix, protectryse both attested from mid-15c. Protectee is attested from c. 1600.
In English history, "one who has care of the kingdom during the king's minority or incapacity, a regent" (as the Duke of Somerset during the reign of Edward VI); Lord Protector was the title of the head of the executive during part of the period of the Commonwealth, held by Oliver Cromwell (1653-58) and Richard Cromwell (1658-59).