Guardian Angels

The belief in Guardian Angels appears in the Old Testament, although it is not specifically articulated. The belief that angels can be guides and intercessors for men appears in the books of Job and Daniel where angels seem to be assigned to certain countries. In the Gospel Jesus says of children: "See that you do not look down on one of these little ones. For I tell you that their angels in heaven always see the face of my Father in heaven." This is often understood to mean that children are protected by guardian angels. In Acts chapter 12 there is another allusion to the belief that a specific angel is assigned to protect each individual. After Peter had been escorted out of prison by an angel, he went to the home of 'Mary the mother of John, also called Mark'. The servant girl, Rhoda, recognized his voice and ran back to tell the group that Peter was there. However the group replied, "It must be his angel."'

The fathers of the Church had differing views on the Guardian Angels. Saint Ambrose, for example, believed that saints lose their guardian angels so that they might have a greater struggle and persevere. Saints Jerome and Basil of Caesarea argued that sin drove the angels away. The first Christian theologian to outline a specific scheme for guardian angels was Honorius. He said that every soul was assigned a guardian angel the moment it was put into a body. St Thomas Aquinas agreed with Honorius and specified that it was the lowest order of angels who served as guardians. Guardian angels appear in literary works throughout the medieval and renaissance periods. 
Popes have always invoked the protection of their Guardian Angels. Pope Pius XI recalled in one of his audiences that he relied on his Guardian Angel’s help when confronting the likes of Hitler and Mussolini. Pope John XXIII in a private conversation with a Canadian bishop attributed the idea of calling an ecumenical council to his Guardian Angel - it was via his Angel that God gave him the inspiration to convene Vatican Council II, which started October 11, 1962, 50 years ago.
One can also name your own Guardian Angels, as I have personally done when I called mine Stephen. Yes, Stephen has been very good to me, protecting me from danger and saving me from near accidents and who knows what else.
PRAYER: Angel of God, my guardian dear, to whom God’s love commits me here, ever this day be at my side, to light and guard, to rule and guide. Amen.