Gabriel the Archangel is one of the few angels given a name in the Bible. He appears in both the Old and New Testaments for a total number of four times.
First, here are the times when he appears in the Bible by name.
1Daniel 8:15-17
2Daniel 9:20-22
3Luke 1:18-20
4Luke 1:26-27
These are the times when Gabriel is mentioned by name. According to the Catholic Encyclopedia, "it is not unreasonable to suppose with Christian tradition that it is he who appeared to St. Joseph and to the shepherds, and also that it was he who 'strengthened' Our Lord in the garden."
These last appearances are not confirmed by the Bible, but are beliefs handed down over the centuries by various saints.