Númenor was the great island kingdom in J.R.R. Tolkien’s legendarium.
The island was raised from the sea by the Valar and given to the Men who had aided the Elves during the wars against Morgoth. Númenor stood in the western ocean between Middle-earth and the Undying Lands, and its people became renowned for long life, seamanship, and power.
Over time, many Númenóreans became resentful of the Elves and jealous of their immortality. Under King Ar-Pharazôn, the kingdom challenged the divine order and attempted to sail against the Valar. The island was then destroyed and submerged in a cataclysm known as the Downfall of Númenor.
Survivors led by Elendil founded the realms of Arnor and Gondor in Middle-earth. Númenor is therefore central to the ancestry and political history surrounding Aragorn, even though most of its story predates The Lord of the Rings.