protector

Short definition from Wiktionary

Noun

1. 1
   Someone who protects or guards, by assignment or on their own initiative.
2. 2
   Someone who protects or guards, by assignment or on their own initiative: A headmate who primarily fronts, or otherwise protects the system, in situations where the system is at risk of psychological harm.
3. 3
   A device or mechanism which is designed to protect.
4. 4
   One who prevents interference.
5. 5
   A state or other subject under international law, exercising a protectorate over another subject in international law.
6. 6
   One having the care of the kingdom during the king's minority; a regent.
7. 7
   A cardinal, from one of the more considerable Roman Catholic nations, who looks after the interests of his people at Rome; also, a cardinal who has the same relation to a college, religious order, etc.