In the one hundred and thirtieth year of the Third Age, Celebrían the wife of Elrond bore twin sons. Dark-haired and grey-eyed, only those that knew them well could tell them apart. The first of the twins was named Elladan, 'Elf-Man' as a token of his ancestry; he was descended not only from the royal houses of the Noldor and the Sindar, but also from the Houses of Hador and Bëor of the Edain.
Many centuries later, the twins' mother Celebrían went on a journey into the south to visit her own mother, Galadriel, in the land of Lórien. In the Redhorn Pass, she was captured by orcs, and tortured in their dens. Elladan rode with his brother to rescue her, but by the time they reached her she had received a poisonous wound. Though their father healed her, she would not remain in Middle-earth, and sailed into the West the following year. After this loss, Elladan and his brother Elrohir were filled with hatred of the orcs, often riding against them with the Northern Dúnedain.
In the early part of the War of the Ring, the brothers' main role was to scout the land and prepare the way for the Fellowship, but later they took a more active part. When Halbarad rode to Aragorn's aid with the Grey Company, Elladan and Elrohir accompanied them. They followed Aragorn through the Paths of the Dead, fought with him at Pelargir, and took part in the Battle of the Pelennor Fields, where they fought with stars bound to their brows.
After the War of the Ring, little is known of the brothers' fate. They returned to their father's house at Rivendell, and remained there even after he had passed across the Sea. Like their sister Arwen, the sons of Elrond Half-elven were granted the choice of whether to leave Middle-earth for the Undying Lands, or remain there and become Mortal as Men. Elladan had such a bond with his brother that they must surely have chosen alike, but what choice they made in the end can never now be known.