A seraph (Hebrew שׂרף, plural שׂרפים Seraphim) is one of a class of celestial beings mentioned once in the Hebrew Bible (Tanakh or Old Testament), in Isaiah. Later Jewish imagery perceived them as having human form, and in that way they passed into the ranks of Christian angels. In the Christian angelic hierarchy, seraphim represent the highest known rank of angels. There are only two angels in the canonized Greek and Hebrew Bible mentioned by name: Michael (who is described as the archangel) and Gabriel.