Known as Elendil the Tall (Tolkien put his height at "more than man high by nearly half a ranga, almost 8'), Elendil the Faithful ('Elendil Voronda' or 'Vorondo') or Elendil the Fair, he was the father of Isildur and Anárion, last lord of Andúnië, and the first High King of Arnor and Gondor.
Elendil, his sons Isildur and Anárion, and their supporters fled to Middle-earth at the downfall of Númenor, sailing east in nine ships and founding the realms of Arnor and Gondor in Middle-earth in S.A. 3320. With them they took the palantíri, the "Seeing Stones" that were given to the Lords of Andúnië by the Elves of Tol Eressëa, and a seedling of Nimloth, the White Tree of Númenor.
Unfinished Tales explains that, upon landing in Middle-earth, Elendil proclaimed in Quenya: "Out of the Great Sea to Middle-earth I am come. In this place will I abide, and my heirs, unto the ending of the world." His heir and 38-great-grandson Aragorn spoke these traditional words again when he took up the crown of Gondor in The Return of the King.
Elendil lived in Arnor, where he founded the city of Annúminas. His son Anárion founded the city of Minas Anor in Anórien, and his son Isildur founded Minas Ithil in Ithilien. Across the Anduin the city of Osgiliath was built. Across the realms, towers were built for the seeing-stones called palantíri, with which the realms kept in contact.
As explained in The Fellowship of the Ring, Sauron eventually returned to Middle-earth, establishing a stronghold in Mordor, which was next to Gondor. In 3428 he attacked, seizing Minas Ithil. Isildur fled north to his father, leaving Anárion in charge of Gondor. In 3434, Elendil and Isildur returned south, together with the Elven High King Gil-galad and their combined armies, in the Last Alliance of Elves and Men. They defeated Sauron in the Battle of Dagorlad, and laid siege to his stronghold of Barad-dûr for seven years. During this long siege Anárion was killed. In the year 3441 of the Second Age, Sauron came out personally to do battle. Gil-galad and Elendil fought him, overthrew him and killed his body, but both were killed as well, and Elendil's sword Narsil was broken beneath him. Isildur used the broken sword to cut the One Ring from Sauron's hand, and the Dark Lord's spirit fled, not to reembody itself in its old form for many years.
The standard of Elendil was the White Tree Nimloth with seven stars above it (representing each of the stars on the banners from the seven of the nine ships that escaped the destruction of Númenor that carried the palantíri), and above them a silver crown. This standard became the main symbol of royalty in Gondor.
In Ralph Bakshi's 1978 animated adaption of The Lord of the Rings, Elendil is only mentioned and not shown. Aragorn mentions that he carries the sword of "Elendil of Gondor", but his relationship with Isildur is not explored.
In Peter Jackson's The Lord of the Rings film trilogy, Elendil is portrayed by Peter McKenzie. He appears in the prologue, where he is killed by Sauron. Though Aragorn uses his name as a battle cry, he is never identified with it.