what was his role as a servant?
He served Aulë the Vala Smith, acquiring much knowledge.
Sauron
Sauron served Aulë the Vala Smith, acquiring much knowledge; he was at first called "Mairon" 
who has a ring of power in lotr Sauron. who is he/she? The title character and the main antagonist of "The Lord of the Rings". is it a series or a novel? A novel in three volumes. who is the author of this novel? J. R. R. Tolkien. has it been adapted in any form? It  has been adapted for film, radio, stage, and television. which war was the main antagonist involved in? War of the Last Alliance.
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Sauron [SEP] Servant of Aulë
Sauron served Aulë the Vala Smith, acquiring much knowledge; he was at first called "Mairon" (Quenya for "the Admirable") until he joined Melkor. In Beleriand, he was called in Sindarin "Gorthu" "Mist of Fear" and "Gorthaur" "The Cruel". Sauron was drawn to the power of Melkor, who attracted him by seeming to have power to "effect his designs quickly and masterfully", as Sauron hated disorder. Sauron became a spy for Melkor in Almaren. Melkor soon destroyed Almaren, and the Valar moved to the Uttermost West: the Blessed Realm of Valinor, still not perceiving Sauron's treachery. Sauron left the Blessed Realm and went to Middle-earth, the central continent of Arda, where Melkor had established his stronghold.