Aragorn II was an heir of Isildur and the twenty-sixth Chieftain of the Dunedain. He was the son of Arathorn II and Gilraen the Fair. Aragorn never really got to know his father, for he died two years after Aragorn was born. Arathorn went hunting for orcs one day and never returned, for he was shot through the eye and died.
Gilraen knew if Aragorn was going to grow up to become a great chieftain like so many of his ancestors, he would need a father. So she took him to Imladris to be fostered by Elrond Half-elven.
There he was named Estel, "Hope", at the bidding of Elrond, for he was hunted by the Enemy, and his true name and lineage could not fall into their hands.
Eighteen years after, Estel had done many good deeds with the sons of Elrond [Elladan and Elrohir], and Elrond was pleased. Elrond took him to his chamber and told him of his name and who he was, and who his father was.
"Here is the ring of Barahir," Elrond said as he gave the token of his kinship to him. Aragorn also received the shards of Narsil, the sword once used by Isildur to cut the One Ring from the hand of Sauron, which had been passed down from heir to heir.
But the Sceptre of AnnÚminas Elrond kept, "For he has yet to earn it."
The next day, Aragorn saw and heard what he believed to be Luthien. "Tinuviel, Tinuviel," he called and the elf maiden looked at him curiously. She told him she was Arwen Undomiel, daughter of Elrond, and Aragorn believed surely that she had been locked up in her father's chamber. She had actually been visiting her mother's kin in Lothlorien, for her mother was Celebrian, the daughter of the Lord and Lady of the Wood.
From then on Aragorn II loved Arwen Undomiel, daughter of Elrond.
Elrond soon learned of this and told Aragorn that he would not have a wife till he had earned it, for he and his mother doubted Aragorn would ever reach so high as to receive Arwen Evenstar as a wife. So Aragorn said farewell to his mother, Elrond, and Arwen.
For the next thirty years he worked in the cause against Sauron, and doing so, met Gandalf the Wise, from whom he gained much wisdom. He always went into different lands in different names and won much renown in all his guises. He served in the hosts of the Rohirrim and fought for the Lord of Gondor. Then he went South-east and explored the hearts of men, good and evil, and the devices of Sauron.
Thus he learned much, and became the most hardy of living men, skilled in crafts and lore. He knew much of the elves and kindled light in his eyes where few could endure.
It came to pass when Aragorn was [forty-nine] years old that he became weary and traveled back to Rivendell, and on his way came to Lothlorien and was allowed entrance by the Lady Galadriel.
There she clothed him in silver and white, and placed a gem on his brow. Then it seemed he was more than a chieftain, yes, more than a man. He appeared to Arwen, whom he did not know was watching him, as an Elf-Lord, and under Caras Galadon Arwen's doom was appointed. And it soon came to pass that Aragorn had to depart, and the two sat upon the fair hill, Cerin Amroth, at twilight and talked of their love.
"'But neither, lady, is the Twilight for me; for I am mortal, and if you will cleave to me, Evenstar, then the Twilight you must also renounce'. And she stood then as still as a white tree, looking into the West, and at last she said: 'I will cleave to you, Dunadan, and turn from the Twilight. Yet there lies the land of my people and the long home of all my kin.'"
When Elrond learned of his daughter's decision he was silent, and he grieved. Aragorn soon returned to Rivendell and Elrond told him that if he were to ever receive Arwen, he would have to become High King of both Gondor and Arnor.
Sauron grew in Barad-dur, and Aragorn went out, while Arwen remained in Rivendell.
Aragorn returned to Rivendell every so often, and on a time his mother, Gilraen, told him that her time to leave Middle-earth was coming. Aragorn asked her to stay and see the light after the darkness, but she replied, "Onen i-Estel Edain, u-chebin estel anim" ("I gave Hope to the Dunedain, I have kept no hope for myself") and she died the next spring.
The year then was 3007, and Aragorn had received word from Gandalf that he might have found the One Ring and needed his help to find Gollum, the Third Ring Bearer. In 3009 and the following seven years Aragorn and Gandalf searched for Gollum throughout the Vales of Anduin, Mirkwood, and Rhovanion without luck. Finally, in 3017, Aragorn caught Gollum in the Dead Marshes and brought him to Mirkwood.
A year after Gandalf returned to the Shire and informed Frodo that he must bear the One Ring to Rivendell, and perhaps farther. Mirkwood was attacked and Gollum ran free again.
Aragorn II went to Bree and waited for Frodo. Under the name "Strider" he found them and led them to Rivendell. In this small journey, he evaded and defended the Hobbits from five nazgul. When Frodo was wounded, Aragorn healed him as well as he could, before handing him to Glorfindel, an Elf-lord of Rivendell.
Aragorn came to the Council of Elrond and Legolas exclaimed that he was Aragorn II, Heir of Isildur [Legolas states this in the movie version for greater conflict. In the book, The Fellowship of the Ring, Elrond answers Boromir's question about who Aragorn is.] Aragorn joined The Fellowship of the Ring, and helped with his sword and his great wisdom and lore.
When Gandalf fell into the pits of Moria, Aragorn led the Fellowship to Lothlorien, and was welcomed.
When Boromir was slain by orcs, Aragorn took an oath to not fail the people and kingdom of Gondor, and pursued the orcs in the evening with Legolas and Gimli to save Merry and Pippin. It was Aragorn who found the first clues to which direction the orcs went, and without his great tracking abilities, the remaining Fellowship would have never gotten as far as they did. They soon came upon a host of Rohirrim, and Aragorn met Eomer, Third Marshall of the Mark, for the first time. Eomer became a good friend to Aragorn, and they fought bravely together at the Battle of Hornburg.
Soon Aragorn made it to Isengard with Legolas, Gimli, Eomer, Gandalf, Theoden, and the large army of Rohan. There he found it had been torn apart by the Ents, and he was greeted merrily by Pippin and Merry, instigators of the attack.
Pippin rode to Gondor after he talked with Sauron through the Palantir, but Merry and Theoden and the rest of Rohan's army went back to Edoras.
Aragorn, being advised to hurry by a message from Elrond delivered by a host of 30 Dunadain plus Elrohir and Elladan, sons of Elrond, took the quicker Paths of the Dead. There he found many dead men who followed him, for he was the Heir of Isildur, the one they betrayed so many years before, and redemption required they help Aragorn. Aragorn, Legolas, Gimli, and the Dunadain came upon the ships of the Corsairs, sailing to Minas Tirith to aid the evil army of the Enemy. He assailed it with the help of those who had come with him and the dead men. He took men from that part of Gondor with him and sailed to Minas Tirith.
At first it seemed to the soldiers of Gondor that reinforcements from Umbar had anchored and were coming to help the Enemy's forces, and if that were the case, Gondor would have certainly lost Minas Tirith, and soon the rest of their land. But Aragorn and his followers came out and slew many orcs, easterlings, haradrim, corsairs and southrons.
The King Elessar had returned.
He marched to the Black Gate, and there he fought in the last battle of the War of the Ring, distracting Sauron from the potentially lethal thrust by Frodo.
Just when the forces of Good were about to lose, Gollum fell into the Cracks of Mount Doom with the One Ring around Frodo's bitten-off finger in his hand. Confusion took over everyone in Mordor.
Sauron was vanquished and Aragorn became the King of Arnor and Gondor. The Shire, he permitted only Hobbits to dwell in, and he and his wife, Arwen Undomiel, lived happily as King and Queen, till the end of their days.