Sauron

Sauron (also known as Gorthaur, Annatar, Artano, Aulendil, the Necromancer) was a Maia and he was Morgoth´s foremost servant. When Morgoth was imprisoned by the other Valar Sauron took control of Angband and Morgoth´s armies. After the War of Wrath, he took the name Annatar and became friends with the elves. Together they made the rings of power.  Sauron betrayed the elves and made the one ring to rule over the others, "One ring to rule them all, One ring to find them, One ring to bring them all and in the darkness bind them". By nine of these rings, he ensnared nine Edain kings of renown, and made them into his most feared servants - the Nazgul. He was the one who corrupted most of the Numenorean population into worshipping Morgoth and tricked Ar-Pharason into waging a senseless war against the Valar. His body was destroyed when the Valar destroyed Numenor and his dark spirit returned to Mordor. There he gathered his armies of all the dark creatures that had escaped doom in earlier days. Mordor then allied itself with the Easterlings, the Variags and the Haradrim. Since that time, he has been referred to as the Second Dark Lord. The Last Alliance of Men and Elves waged war against Sauron and his allies in the end of the Second Age. The Siege of Barad-Dur, Sauron's fortress, lasted for seven torturous years. Aragorn's ancestor Isildur took the ring from Sauron but lost it in the river of Anduin. Sauron rose to power once again in the Second Age and started the War of the Ring. When the ring was destroyed in Orodruin Sauron was deprived forever of his body and his power, becoming a mere spirit doomed to gnaw itself in the dark because of his inability to reincarnate.