A guardian angel

Is a type of angel that is assigned to protect and guide a particular person, group or nation. Belief in tutelary beings can be traced throughout all antiquity. The idea of angels that guard over people played a major role in Ancient Judaism. In Christianity, the hierarchy of angels was extensively developed in the 5th century by Pseudo-Dionysius the Areopagite. The theology of angels and tutelary spirits has undergone many changes since the 5th century. The belief is that guardian angels serve to protect whichever person God assigns them to. In ancient Greece, the term angel characterized someone who transmitted news and information. Angels are supernatural beings found in many religions. Angels are usually the mediating step between the transcendental and the secular realms. In Western religions, good spirits are called angels, while evil spirits are called demons. The term angel can mean one who brings news, or invisible beings who transmit news or liturgical spirits.  

Source Wikipedia