Gabriel (meaning "God is my strength" in Hebrew) is an Angel, Mentioned both in the Old and New Testament, who is called upon to bring both prophecies and announce the birth of God's anointed servants.
He makes his first appearance in the Bible when he visits the prophet Daniel to interpret a vision given to him by God. He later reveals to Daniel the prophecy found concerning the future of Israel. It is assumed that he was the angel that was withstood for 21 days by the demonic Prince of Persia but managed to break through with assistance from the archangel Michael.
Centuries later, as recorded in Luke's gospel, Gabriel announces the birth of John the Baptist to Zechariah. And finally, God sends Gabriel to Nazareth in Galilee to a virgin engaged to a man whose name was Joseph, of the House of David.