Boromir is the elder son of Denethor II, steward of Gondor. Boromir is a valiant soldier and high captain of the guard of the city and also greatly dedicated to the protection of his younger brother Faramir. As a testament to their strength the two brothers along with two remaining soldiers held the pass of Osgiliath against the Witch King of Angmar and at the last lept down to into the great River Anduin and swam safely to shore as the bridge was cast down and the western shore thus held safe against the Enemy. The bridge was not taken again until the time of the Battle of the Pelennor Fields in The Return of The King in which Sauron moved the bulk of his (not yet fully mustered) army upon the city of Minas Tirith, the last great bastion of free men in Middle-Earth.
Boromir shared a prophetic dream with his brother of the coming of doom and the time of the great plans to be set in motion that could not be denied. While at the Council of Elrond, Boromir shares the words of his (and his brother's) dream:
(The Lord of the Rings: The Fellowship of the Ring, The Council of Elrond, page 296)
"In that dream I thought the eastern sky grew dark and there was a growing thunder, but in the West a pale light lingered, and out of it I heard a voice, remote but clear, crying:
Seek for the Sword that was broken:
In Imladris it dwells;
There shall be counsels taken,
Stronger than Morgul-spells.
There shall be shown a token,
That Doom is near at hand,
For Isildur's Bane shall waken,
And the Halfling forth shall stand."
From Rivendell the wholly formed fellowship set out. Gandalf sets out with the party as council and leader. Representing the race of men were Boromir and Aragorn. For the race of the elves went Legolas from Mirkwood. For the dwarves went Gimli son of Gloin (whom Bilbo traveled with in The Hobbit) and the tightly knit hobbit friends Frodo, Sam, Merry, and Pippin make up the last four members of the party set against the nine riders of Mordor.
Boromir proves his worth on the Pass of Caradhras (Redhorn Gate) as the fellowship attempted to pass over the Misty Mountains. The company was set upon by severe snowstorms which proceeded to block the path behind them that they wished to reuse to attempt the passage toward Moria, being a man of large stature and strength Boromir began walking and heaving snow clearing a path for the fellowship. Shortly thereafter joined in his effort by Aragorn before long the two had cleared a long stretch of the path with only a few yards remaining which Legolas points out to them after walking swiftly atop the high drifts.
Aragorn and Boromir each pack the hobbits through the path and safely to the clearing where their attempt at passing Caradhras ends.
The fellowship then elect (much to Boromir's objection) to take the passage of Moria where Gimli's cousin Balin (another of Bilbo's earlier traveling companions from The Hobbit) went years ago to reclaim for the dwarves since it's loss to the goblins in the dark years. From the wilderness about them before reaching the West Gate of Moria the company hears the howling of the wargs and are attacked. The company fights valiantly and Boromir hews the head from one of the great beasts and with the help of Gandalf's magic the party escapes and Boromir then goes elects to go along with the decision of the fellowship to take the path of the mines.
This quest proved dark from it's beginning with the attack on Frodo by the Watcher in the water of the dammed pool outside the Gates of Moria. As the fellowship fled into the mines the Watcher closes the Great Gate and the sound as if of falling stone is faintly heard outside and figuring the path is of no more use to them the fellowship proceeds on deeper into the mines. As their journey through the mines progressed the fellowship came upon the tomb of Balin where they are attacked again by orcs of the mountains. At the conclusion of the battle the party flees through the east door and Gandalf seals the door with a spell as a great light breaks violently against it cracking the wall as they flee. As the fellowship make their final dash across the Bridge of Khazad-dum they are attacked by a balrog, a demon in the early days of Middle-Earth served Melkor (Morgoth) and were believed to now be gone from Middle-Earth forever. As Gandalf makes a last stand against the demon on the bridge Aragorn and Boromir stand at the end of the bridge behind Gandalf and Boromir lets loose a deep and loud blast from the Horn of Gondor which gives pause to the enemy and all is suddenly quiet for a few moments. It is however to no avail and Gandalf is taken into the void along with the balrog and the company obey his final order and flee from the mines to safety.
From this "defeat" the fellowship under the leadership of Aragorn make for the woods of Lothlorien. After entering Lothlorien the group are taken to the heart of the elven kingdom where they are introduced to the Lord Celeborn and the Lady Galadriel. Galadriel peers into the heart of each member of the company and finds their deepest/truest intentions and desires. Here Boromir's desire for the power and dominant capability of the One to be used against the Enemy are made known to her. Through the companies stay at Lorien, Boromir finds no comfort or rest in the tranquility of the haven they are offered. From their very entrance of Lorien, Boromir is made suspect by Frodo and his actions and intentions become more and more questionable. At the beach of Amon-Hen the company seeks their next course of action and Frodo asks for an hour to be alone and come to his final decision. Boromir follows Frodo and in a fit of rage attempts to take the One from Frodo but Frodo slips it on and vanishes. Beaten and regretful of his actions Boromir slinks back to the party where his actions are found out and upon hearing that Frodo put on the One the company scatters in an attempt to find him. Frodo makes his way to the boats and and Sam (guessing his intentions) breaks off from following Aragorn and makes for the boats to follow his master.
Aragorn tells Boromir to go after Merry and Pippin and when Boromir does find them the two young hobbits have been surrounded by a party of orcs (Uruks). Boromir fought bravely and truly but arrow after arrow finally brings down the mighty warrior and Merry and Pippin are captured and taken away. When Boromir is found amidst the scores of enemies he had felled by Aragorn, he is still alive with his sword broken near the hilt and his horn is cloven in two. Aragorn promises that Minas Tirith will not fall to the Enemy. After his death the remaining members of the fellowship (Aragorn, Legolas, and Gimli) arrange Boromir's body in one of the boats given to them by Galadriel with his weapons, the weapons of his enemies as well as his personal items and then commence Boromir's body to the river and over the mighty Falls of Rauros.
Faramir later claims that as if in the haze of a dream he found one part of his brother's cloven horn upon the beach and watched as the boat that carried the body of Boromir passed by him in the river and carried on toward the great sea.