The History of the Numenoreans: The Second Age of the Sun
Sauron, the Maia, was seduced by Morgoth before the creation of the world, was his most terrible and most trusted servant. After the defeat of Morgoth in the War of Wrath, Sauron assumed a fair form in fear of the Valar.
After the first age, the Valar created an isle for the men who had fought against Morgoth. This isle was named Numenor. Also, the Valar, who could not take away Man's "gift" of mortality, did elongate the length of time of the Numenorean's lives. Over many centuries, the Numenoreans grew great in power and knowledge. However, throughout the lines of the Kings of Numenor, they ever grew jealous of the seemingly immortality of the elves. In time the Numenoreans came to the shores of Middle-Earth, to the east of Numenor. In the earliest times the Numenoreans ventured into Middle-Earth, they befriended Gil-Galad, the last High King of the Noldor in Middle-Earth. Then, Sauron, with even all his hoardes of orcs and goblins, could not stand up to the might of the Numenoreans, and so, Sauron presented himself to the Numenoreans as hostage. However, this was the downfall of Numenor. After a time, had become the most trusted of Ar-Pharazon, the then King of Numenor. By this time, the people were split into two factions. Those who still befriended the elves called the Faithful, and those called the King's Men. Sauron turned the King and his Men against the elves and the Valar. 
The Numenoreans sought the Blessed Realm where they, since given the Isle of Numenor, weren�t allowed to go. They sought endless life they thought could elongate their lives. The Valar at this time, laid down their governance of Arda and Eru, the One, reformed the world. In this reformation, the fleets, that had set sail for Valinor, were drowned, and the Isle itself toppled and sank beneath the waves. Only Elendil and his sons escaped. They were of the line of Elros, the first King. Elendil and his sons landed in Middle-Earth and founded the realm of Gondor.
In secret, after the drowning of Numenor, Sauron had also come back to his former stronghold in Mordor. By this time, Sauron was named the Enemy and Dark Lord. He was not defeated until Frodo destroyed the Ring at the end of the Third Age.
The Second Age of the Sun did not end until Sauron's first defeat against Elendil, his sons, and Gil-galad.
