A spiritual messenger created by God as a way to communicate with human beings. They are also guardians, warriors, judges, and guides.
Angels are most commonly depicted in the form of a human with bird-like wings of white or gold, they may have a halo over the head or surrounding the entire body. They also appear in the form of fire, lightning, and clouds, have the power of invisibility and may appear or disappear suddenly, they are immortal and they can fly.
While they may appear male or female, truly they are spirits, bodiless and sexless.
They are divine beings blessed with great wisdom and the ability to pass judgement correctly, but they are not without fault.
If they lapse into sin and are caste out of heaven they are known as fallen angels, if they choose to turn away from God, they become demons.
According to the Holy Bible, the Lord said "I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things." (Isaiah 45:7)
From this Gustav Davidson determines that "Evil itself is an instrumentality of the Creator, who uses evil for his own divine, if unsearchable, ends." and further gathers that all angels are serving God even when they're following the direct orders of the Devil.
See Also: Creatures by Type » Angels
The Holy Bible, King James Version.
Davidson, Gustav. A Dictionary of Angels. New York: The Free Press, 1967.