A guardian angel is an angel who protects and guides a particular person. The concept of tutelary angels and their hierarchy was extensively developed in Christianity in the 5th century by Pseudo-Dionysius the Areopagite. The theology of angels, and tutelary spirits, has undergone many refinements since the 400s, and belief in both the eastern and western churches is that guardian angels protect whichever person to whom God assigns them and present prayers to God on that person's behalf. The Roman Catholic Church's calendar of saints includes a memorial for the guardian angels on October 2