A traditional prayer for rain, recited on this week’s holiday of Shmini Atzeret, invokes a mysterious angel named Af-Bri. It seems this angel is the joint product of a 6th- or 7th-century poetic genius, Eleazar Kalir, and a particularly recondite verse in the book of Job. According to Philologos:
In the sense of an angel, [the name Af-Bri] seems to have originated with Kalir himself—or at least there is no older source to which it can be traced. But the word af-bri can be found in one place in the Bible, in the book of Job. There, in Chapter 37, in a passage describing God’s rain- and storm-making powers, there is a verse that reads in Hebrew “Af-bri yatriah av, yafitz anan oro.” In English this can be translated as— well, if anyone knew for sure how to translate it, we wouldn’t need angels to help us out.
Kalir . . . clearly was not satisfied with any of the explanations of af-bri that were known to him, and so he came up with one of his own—to wit, that an angel called Af-Bri made the rain clouds. A belief in angels who performed God’s bidding and administered various aspects of Creation was all but universal in Kalir’s day, both in Judaism and other religions, and although Af-Bri would have been an unusual name for an angel, the idea of a celestial being responsible for precipitation would not have seemed outrageous.