A person or thing that protects someone or something from harm or danger. The knight served as a protector of the realm, defending it from invaders.
A device or implement that provides protection. The screen protector on my phone prevents scratches on the display.
A person who is responsible for the care and protection of someone, especially a child or a vulnerable person. As a legal guardian, she was the protector of her younger siblings.
Historical. A person who rules or governs a country as a regent or head of state. Oliver Cromwell became Lord Protector of England in 1653.