Gabriel was an angel who, according to the Bible, served as a messenger of God. In the Christian faith, he is said to be one of three archangels ("highest of angels").
In 2267, Dr. McCoy quipped that just once he would like to transport down to a primitive planet and say, "Behold, I am the Archangel Gabriel!"
Spock, however, did not find any humor in breaking the Prime Directive, to which McCoy agreeably retorted "You could hardly claim to be an angel with those pointed ears, but say you landed someplace with a pitchfork", noting Spock's apparent physical similarities to the Devil. (TOS: "Bread and Circuses")