Elros was the twin brother of Elrond, the sons of Eärendil and Elwing, and so a descendant of Elves, Men and Maiar alike. At the end of the First Age the Valar gave the two the choice of which kindred they would belong to, and Elros chose to be numbered among Men, with the lot of mortality that went with it.1
When the War of Wrath was over, the Edain who had fought against Morgoth were given an island in the western sea, Númenórë, raised from the deeps by the Valar, and a gift of long life. Elros led them across the sea, and was the first of their Kings, taking the name Tar-Minyatur in Quenya.2
He reigned for four hundred and ten years, and lived to be five hundred, a span many times that of ordinary Men. His life ended at last in the year 442 of the Second Age, and the Númenóreans honoured him as the founder of their house.2,3
His brother Elrond chose the Elven lot and remained in Middle-earth. Every King of Númenor after Elros, and every heir of Isildur down to Aragorn, was counted of his line, which is why the Dúnedain kept a family tree running back to him through the long years of their decline.2,4
Sources
Citations name the chapter rather than the page, so they work in any edition. The colour of each note shows what kind of source it is.
- Appendices Tolkien's own appendices to The Lord of the Rings.
- Edited posthumously The Silmarillion, Unfinished Tales and Tolkien's late writings on the Elder Days, assembled by Christopher Tolkien from his father's papers.
- Edited posthumously The Silmarillion, Quenta Silmarillion, ch. 24, “Of the Voyage of Eärendil and the War of Wrath”
- Edited posthumously The Silmarillion, “Akallabêth”
- Appendices The Lord of the Rings, Appendix B, “The Second Age”
- Appendices The Lord of the Rings, Appendix A, I (i), “The Númenórean Kings”