"Elrond of Rivendell is of that Kin."
Elrond's Family Tree - Credit: Victoria Hooper
In Tolkien’s world there are only three mortal men ever to have married elves, and all the half-elven can be found in the same family tree. The half-elven Eärendil was the son of the elf Idril and the man Tuor. He married Elwing, the grand-daughter of the elf Lúthien and the man Beren. Eärendil and Elwing’s children were Elrond and Elros. These two were given the choice of whether they would like to embrace their mortal side, or continue to live among the elves. Elrond chose his elvish side and immortal life (he is now over 6000 years old) . Elros chose to be mortal, and became the first of the Númenorian Kings. Aragorn (Strider) is descended from Elros’ line. Elrond’s daughter, Arwen, is also half-elven and she too has been faced with the choice of whether to embrace mortal or immortal existence. Her choice is told in the appendices of Return of the King
N.B. ‘Half-elven’ refers to any elf descended from men and elves, rather than those who are literally half-elf. E.g. Elrond Halfelven is actually 3/8th man, 9/16th elf, and 1/16th maiar!
Wikipedia’s Half-Elven Family Tree