Metatron is unlike the other figures in this listing in a specific way: he has a biography, and it begins with him not being an angel.
The identification is with Enoch, of whom Genesis says only that he walked with God and was not, for God took him. The pseudepigraphic literature elaborated that silence at length, and 3 Enoch, the Hebrew apocalypse belonging to the Hekhalot corpus, gives the fullest form: Enoch is taken up, his body transformed to fire, and he is enthroned as Metatron, given seventy names, set over the heavenly household, and titled the lesser YHWH.
That last title is the reason the figure matters beyond angelology. A second figure bearing the divine name, seated in heaven, is difficult to reconcile with strict monotheism, and the rabbinic literature registers the difficulty directly. The Talmudic passage at Hagigah 15a tells of Elisha ben Abuyah, who ascends, sees Metatron seated, when angels are understood not to sit, and concludes that there are two powers in heaven. He becomes the archetypal apostate, known thereafter as Aher, the Other. In the story Metatron is given sixty lashes of fire to establish that he is a servant and not a second god.
Andrei Orlov's study traces how the Enoch traditions produced this figure, and Gershom Scholem treated the passage as evidence of an internal Jewish argument about heavenly mediation rather than a polemic against outsiders. The narrative does the theological work: it does not deny that Metatron is exalted, it establishes that the exaltation is delegated. The lashes are the point.
The placement of Metatron at Kether in the arrangement recorded here belongs to the later Kabbalistic and ceremonial systems rather than to the Hekhalot material, where he has no sephirotic position because the sephirot as later understood are not yet in place. The pairing with Sandalphon at Malkuth, the two of them as the top and bottom of the Tree and sometimes described as brothers, is later still and is a symmetry of the system rather than an inheritance from the sources.
The transformation of a human being into the highest of the angels has no parallel among the others listed here, all of whom are angels from the start. It is also the point at which angelology stops being a catalogue and becomes an argument about what heaven contains.