Gwaith-i-Mírdain
From Tolkien Gateway
Gwaith-i-Mírdain was a brotherhood formed by Celebrimbor and the other master-craftsmen of Eregion. They were said to be the most skilled artisans to have worked since the time of Fëanor himself (who was indeed Celebrimbor's grandfather). Their skill was subverted by Sauron, in the guise of Annatar the "Lord of Gifts", who turned their abilities to the making of the Rings of Power.