A shoulder angel is a plot device used for dramatic and/or humorous effect in fiction, mainly in animation and comic books/strips. The angel represents conscience and is often accompanied by a shoulder devil representing temptation. They are a useful convention for depicting the inner conflict of a character.
After Guido Reni
A guardian angel in a 19th-century print
Isaac Blessing Jacob by Gerbrand van den Eeckhout; at the MET
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.
Icon of a guardian angel
Guardian Angel by Pietro da Cortona, 1656
A guardian angel in a 19th-century print by Fridolin Leiber
Guarding angel on a c. 100-year-old tankard