A pure spirit created by God, immortal spiritual beings, having intelligence, power, and free will, they act as messengers and ministers of his will. Referred to in both the Old and New Testament. Scripture gives no indication of the time of their creation. Jesus often speaks of angels in the New Testament. They are numerous, and nine classes exist: The New Testament mentions Angels, Powers, Virtues, Principalities, Dominations, Thrones, and Archangels. The Old Testament also mentions Cherubim and Seraphim. Both Old and New Testaments refer to the fall of many angels.

Bible References

Three Angels mentioned by name in canonical Scriptures:

St. Gabriel - 4 times*

In Daniel 8, he explains the vision of the horned ram as portending the destruction of the Persian Empire by the Macedonian Alexander the Great, after whose death the kingdom will be divided up among his generals, from one of whom will spring Antiochus Epiphanes.

In chapter 9, after Daniel had prayed for Israel, we read that "the man Gabriel . . . . flying swiftly touched me" and he communicated to him the mysterious prophecy of the "seventy weeks" of years which should elapse before the coming of Christ. In chapter 10, it is not clear whether the angel is Gabriel or not, but at any rate we may apply to him the marvelous description in verses 5 and 6.

In the New Testament he foretells to Zachary the birth of the Precursor, and to Mary that of the Savior.

St. Michael - 4 times*

St. Michael is one of the principal angels; his name was the war-cry of the good angels in the battle fought in heaven against the enemy and his followers.  

Daniel 10:13,  Gabriel says to Daniel, when he asks God to permit the Jews to return to Jerusalem: "The Angel [D.V. prince] of the kingdom of the Persians resisted me . . . and, behold Michael, one of the chief princes, came to help me . . . and none is my helper in all these things, but Michael your prince";

Daniel 12, the Angel speaking of the end of the world and the Antichrist says: "At that time shall Michael rise up, the great prince, who standeth for the children of thy people."

In St. Jude: "When Michael the Archangel, disputing with the devil, contended about the body of Moses." St. Jude alludes to an ancient Jewish tradition of a dispute between Michael and Satan over the body of Moses, an account of which is also found in the apocryphal book on the assumption of Moses. St. Michael concealed the tomb of Moses; Satan, however, by disclosing it, tried to seduce the Jewish people to the sin of hero-worship. St. Michael also guards the body of Eve, according to the "Revelation of Moses" ("Apocryphal Gospels", etc., ed. A. Walker, Edinburgh, p. 647).

Apocalypse 12:7, "And there was a great battle in heaven, Michael and his angels fought with the dragon." St. John speaks of the great conflict at the end of time, which reflects also the battle in heaven at the beginning of time. According to the Fathers there is often question of St. Michael in Scripture where his name is not mentioned. They say he was the cherub who stood at the gate of paradise, "to keep the way of the tree of life" (Genesis 3:24), the angel through whom God published the Decalogue to his chosen people, the angel who stood in the way against Balaam (Numbers 22:22), the angel who routed the army of Sennacherib (2 Kings 19:35).

Saint Michael, the Archangel

Christian tradition gives to St. Michael four offices:

To fight against Satan.

To rescue the souls of the faithful from the power of the enemy, especially at the hour of death.

To be the champion of God's people, the Jews in the Old Law, the Christians in the New Testament; therefore he was the patron of the Church, and of the orders of knights during the Middle Ages.

To call away from earth and bring men's souls to judgment .

Regarding his rank in the celestial hierarchy opinions vary; St. Basil and other Greek Fathers, also Salmeron, Bellarmine, etc., place St. Michael over all the angels; they say he is called "archangel" because he is the prince of the other angels; others (P. Bonaventura) believe that he is the prince of the seraphim, the first of the nine angelic orders. But, according to St. Thomas he is the prince of the last and lowest choir, the angels. The Roman Liturgy seems to follow the Greek Fathers. The hymn of the Mozarabic Breviary places St. Michael even above the Twenty-four Elders. The Greek Liturgy styles him Archistrategos, "highest general."

St. Rafael (God has healed")*

Appears in the Book of Tobias. Here he first appears disguised in human form as the traveling companion of the younger Tobias, calling himself "Azarias the son of the great Ananias". The story of the adventurous journey during which the protective influence of the angel is shown in many ways including the binding "in the desert of upper Egypt" of the demon who had previously slain seven husbands of Sara, daughter of Raguel, is picturesquely related in Tobit 5-11, to which the reader is referred. After the return and the healing of the blindness of the elder Tobias, Azarias makes himself known as "the angel Raphael, one of the seven, who stand before the Lord" (Tobit 12:15. Cf. Revelation 8:2

Of these seven "archangels" which appear in the angelology of post-Exilic Judaism, only three, Gabriel, Michael and Raphael, are mentioned in the canonical Scriptures. The others, according to the Book of Enoch are Uriel, Raguel, Sariel, and Jerahmeel, while from other apocryphal sources we get the variant names Izidkiel, Hanael, and Kepharel instead of the last three in the other list.

Guardian Angels

Angels assigned by God to each person to protect and guide that soul throughout life on earth. Although guardian angels are accepted by theologians, the church has never defined them as being part of the article of faith. The Church approves the devotion to guardian angels, as evidenced by the fact Pope Clement X named October 2nd  the feast of the guardian angles. NewAdvent.org has a very detailed discussion.