The Númenoreans were a race of Men, described in the works of the author J.R.R. Tolkien. Although mentioned little in his most famous work, The Lord of the Rings, the Númenoreans were the strongest race of Men ever to inhabit Middle-earth.
At the end of the First Age of the Sun, the power of the dark enemy Morgoth (the Elvish name for Melkor) had been broken in the terrible Wars of Beleriand. These battles concluded, there remained a small fraction of the race of Men known as the Edain, allies of the Elves against Morgoth. The Valar took pity on the remnant Edain and created a great island nation for them in the Western Sea, between Middle-earth and the Undying Lands. With this land came the gift of long life and great strength of mind and body, almost equaling that of the Elves. Over time, the Edain expanded and evolved into the race that became the Númenoreans, their land named Númenor, or Westernesse. Other names for the island include Andar, "the Land of Gift"; Elenna, "the Land of the Star"; and Mar-nu-Falmar of Atlante.
First of the Kings of Númenor was Elros Halfelven, brother to Elrond who later ruled the Elvish region of Rivendell. However, where his brother chose to follow the immortal life of the Elves, Elros chose to become mortal. Despite this, Elros still reigned 400 years. In his native tongue he was known as Tar-Minyatur. Sailing was the Númenoreans' greatest skill, and they sailed farther than any race ever to walk the face of Arda, even as far as the Gates of Morning in the East. However, they were never able to sail Westwards; the Powers of Arda had long decreed that no mortal could ever tread the soil of the Undying Lands of Eldamar and Valinor.
As time passed, the fortunes of the Men of Númenor increased, and their race grew prosperous. However, this golden age was overshadowed as darkness rose again in Middle-earth. Although Melkor was defeated, his chief servant, the Dark Lord Sauron, had returned in force and began marshaling forces in the South and East. Amongst his Orc and Troll armies, Men of the Haradrim and Dunlendings joined his cause. It was at this time the Rings of Power were forged, and the Nazgûl first came into being. Sauron, backed by the forces of the Nine, made swift war upon the Elves, barely considering the forces of Númenor to be worth fighting. Sauron destroyed the majority of the Elvish settlements, reducing their race even further from its fall during the First Age of the Sun.
However, Sauron's disregard for the power of Númenor cost him, as the great armies of Men rallied to the aid of the beseiged Elves. Sauron's armies in the Western lands were swiftly crushed, and there was peace for a time. The strength of the Númenoreans increased further, as they built the great ports of Umbar in the South and Pelargir in the North. Unfortunately, their pride in their strength, then unrivaled in Middle-earth, led them to declare themselves lords of the land as well as lords of the sea. To this end, in the year 3262 of the Second Age of the Sun the Númenoreans gathered a mighty host of arms, and marched directly on the land of Mordor, where Sauron still reigned. To the astonishment of all, Sauron left his Dark Tower and surrendered immediately; his forces were a fraction of those summoned by his enemies. He was made a prisoner and taken in chains to the King of Númenor, Ar-Pharazon the Golden.
However, this surrender was false; a mere ploy by Sauron to gain by guile what he could not gain by force of arms. He perceived their pride as their greatest flaw, and with it he played on their ambition to prove themselves masters of Middle-earth. Soon he had access to the King of Númenor as his trusted advisor, and shortly thereafter the King fell under Sauron's control. Temples to the Dark Lord were built throughout the land of Númenor, and human sacrifice made on his altar. Unsatisfied with their 'victory' over the Dark Lord, the now warlike Númenoreans wanted someone else to fight. They turned to Sauron, who promptly directed their attention towards the distant Western shore - the forbidden Undying Lands, home to the Powers of Arda.
The Númenoreans assembled the greatest single fleet to ever sail the seas of Arda, and sailed into the West to make war on the Valar. Passing through the Enchanted Isles and the Shadowy Sea, the fleet approached the shores of Valinor. As the great Navy reached the shores, the 'Akallabêth' tells of a great doom that suddenly and swiftly fell upon the world. Though they came to conquer, their first step upon the soil of Valinor brought the Pelori Mountains down upon the Númenoreans and their vast armada. To a man, the Númenoreans were comprehensively destroyed. However, this was only the beginning of the tragedy, for a greater disaster was to follow. The seas rose up, as Meneltarma - the mountain that formed the centre of the Land of Númenor, erupted. Numenor was wiped clean of cities and the remaining Men, before sinking entirely into Belegaer, the Great Sea.
This catastrophe led to the Change of the World, in 3319 (Second Age). The Undying Lands were taken beyond the Circles of the World, out of reach of all but the Elvish ships sailing the Straight Way between the Spheres of both Worlds. Despite this, a small fraction of the Númenoreans survived, fleeing the sinking Númenor by ship and sailing to Middle-earth. These were the 'Elendili', the 'faithful', not corrupted by the influence of Sauron and hence not pursued by the Valar. They had refused to abandon the ancient ways of the Valar and the Eldar. These people sailed to Middle-earth in nine great ships, and formed the Kingdoms of Gondor and Arnor. Others that survived settled in the land of Umbar, eventually turning to evil as the Black Númenoreans.