protector

noun

1. a person or thing that protects; guardian; defender
2. Eng. History
   1. a person ruling a kingdom during the minority, absence, or incapacity of the sovereign
   2. the title held by Oliver Cromwell (1653-58) and his son Richard (1658-59), during the British Protectorate
      in full Lord Protector

Origin: ME protectour < MFr < LL protector