The most powerful Ainu, who wanted to bring things into the Void, a place where he hung out alone in. He sang a different song from that of Illuvitar, much to his creator's dismay, which would go on to create the Children of Iluvatar, elves (Quendi) and men (Atani). He also desired the world for his own, but was overthrown by the Valar.
The Eldar were created shortly after, which were another race of elves (and the name was given to them by Orome). The Eldar traveled to Valinor to live with the Valar.