Numenor:
Isildur was born in Numenor, the elder son of Elendil.
In Numenor as a young man, Isildur saved a fruit of the White
Tree, Nimloth the Fair, at great risk. He had listened quietly as his grandfather, Amandil, warned Elendil that Sauron was working on King Ar-Pharazon to have the White Tree cut down, "for it was a memorial of the Eldar and of the light of Valinor".
Isildur said no word, but that night he went out in disguise. Thus he
went to Armenelos and the courts of the King, a place forbidden to the
Faithful, and came to the place of the tree, forbidden by Sauron to all
and watched day and night by Sauron's guards. Since it was nearly
winter, Nimloth bore no bloom and gave no light, and Isildur managed to
pass the guards in the dark. Isildur took a fruit from the tree but, as
he turned to go, the guards attacked him. He fought his way out,
receiving many wounds, but none knew who had taken the fruit. Isildur
returned to Romenna and delivered the fruit to Amandil, before his
strength failed him. The fruit was planted, and Amandil blessed it.
After it put out its first leaf, Isildur finally arose and was no
longer troubled by his wounds.
Soon after Isildur's foray, Nimloth was cut down and
burned on an altar to Melkor, making a cloud over the land for seven
days until it slowly passed to the west. The young tree was kept on
Isildur's ship with the other ships of the Faithful waiting in the east
of Numenor, along with the seven Palantiri stones gifted by the elves.
Ar-Pharazon took his fleet to Valinor, to force the giving of eternal
life within the Circles of the World, and Manwe turned the fate of the
Children of Eru over to Eru, who destroyed the ships, buried under
falling hills those who had come to shore, and changed the shape of
things so that instead of flat, the world was round, while Aman and
Eressea remained on the flat, reachable only by special means. Sauron
lost his body and could never again assume a form fair to the eyes of
men, traveling as a shadow and wind to Mordor where he took up his Ring
again in Barad-dur, and made himself a new guise.
Isildur escaped the drowning of Numenor in ships with others of the Faithful including his younger brother, Anarion,
in a small fleet commanded by Elendil. As Numenor drowned, Elendil's
grief prevented his ability to command, and the great winds caught up
the nine ships, snapping masts in their power, and cast them to the
vastly changed Middle-earth.
Middle-earth:
Elendil made a kingdom in Arnor and Gondor, sending
his two sons to handle the south kingdom of Gondor while he remained as
High King in Arnor.
The Argonath stone pillars were carved as a boundary
marker, showing the two sons and joint kings, Isildur and Anarion. It
was located on the Anduin River at the entrance to the northern
boundary of Gondor and were seen by the Fellowship of the Ring and
their leader, Aragorn, the Heir of Isildur.
Isildur was the Joint King of
Gondor,
the Lord
of Ithilien, and he founded Minas Ithil. After Elendil's death, he was
High King of Arnor and Gondor. His sons were Elendur, Aratan,
Ciryon, and Valandil.
Isildur fought
in the Last Alliance against Sauron. Isildur's big mistake was that after he cut
the One Ring from Sauron's finger, he took it for himself instead of destroying it.
Isildur was killed in T.A. 2, losing the One Ring in the Anduin River.
He was succeeded by his only surviving son, Valandil.
References: Return of the King:
Appendix A
Appendix B: timeline Silmarillion: "Akallabeth". Ballantine paperback 1977:
pp336-338, 342 for the story of the White Tree.
pp 344-346 for the drowning of Numenor.
pp 347 for Sauron's fate.
Index of Names: Argonath Fellowship of the Ring, Houghton-Mifflin trade movie cover, 1994.
"The Great River" p383 for the Argonath top