A skilled smith in Valinor, Mahtan learned the arts of metal and stone work under the Vala Aul , and for this Mahtan was also called Aulendur, or "Servant of Aul ". He wore a copper circlet around his head and was known for his fondness for the metal. Mahtan in turn taught F anor, the greatest of all Elven craftsmen, who — to Mahtan's regret — used this knowledge to forge the first weapons and armour in Valinor.
Mahtan had a beard, which was unusual for an Elf — especially one as young as he. According to J. R. R. Tolkien most Elves could only grow beards from the "third cycle" of their lives, while Mahtan was an exception in being only early in his second. It is unclear what these "cycles" actually refer to.
Like Melian did for Thingol, perhaps Huan too assumed a permanent body subject to death and all that for love of Celegorm.
Perhaps he erred somehow as a Maia and repented, and so was put under the service of an Oromendur (possibly a valid term, Aulendur is, 'servant of Aule') to prove his good faith.
Either way we have here a Maia, perhaps the only one, who followed the Noldor into Exile and was entangled in the Curse of Mandos.