In the Lord of the Rings trilogy, Boromir is the son of Denethor, the current Steward of Gondor. Boromir is first seen in Rivendell in The Fellowship of the Ring, prior to/during the Council of Elrond (movie/book).
During the Council of Elrond, Boromir tried to convince the council members to send the One Ring to Minas Tirith, where he believed that it could be used as a weapon against the forces of Sauron. The council believed otherwise, believing that Sauron would be able to detect the Ring's presence there.
Soon thereafter, Boromir joined the Fellowship of the Ring in their quest to destroy the One Ring. During the Fellowship's journey to the Misty Mountains and the Mines of Moria, Boromir did what he could to help and protect the others in the Fellowship: digging a path through the snow while on the slopes of Caradhras and fighting the nameless terror at the entrance of the Gates of Moria.
Inside Moria, Boromir fought against the various goblins that had overtaken the realm of Moria. One of the most notable fights was in Balin's Tomb. Soon thereafter, Boromir and the others were forced to flee as Gandalf fell in battle with the Balrog.
After escaping Moria, Boromir and the Fellowship made their way to Lothlorien, where Boromir was disturbed by Galadriel's testing of his mind. While we don't know exactly what went on in his mind at this meeting, we know that he was distracted and at times preoccupied by bringing the Ring to Gondor.
Things came to a head at Parth Galen, near the Falls of Rauros. Here, Boromir finally succumbed to the temptation to take the Ring for himself. "True-hearted Men, they will not be corrupted. We of Minas Tirith have been staunch through long years of trial. We do not desire the power of wizard-lords, only strength to defend ourselves, strength in a just cause. And behold! In our need chance brings to light the Ring of Power. It is a gift, I say; a gift to the foes of Mordor. It is mad not to use it, to use the power of the Enemy against him. The fearless, the ruthless, these alone will achieve victory. What could not a warrior do in this hour, a great leader? What could not Aragorn do? Or if he refuses, why not Boromir? The Ring would give me power of Command. How I would drive the hosts of Mordor, and all men would flock to my banner!"
After seeing that Frodo remained unconvinced, Boromir commanded Frodo to relinquish the Ring. When Frodo refused, Boromir attempted to take the Ring by force. Frodo put on the Ring and fled. Boromir, realizing what had just happened, repented of his actions and wept, calling for Frodo's forgiveness.
Boromir returned to camp, and when asked about what had happened, he explained that he and Frodo had an argument, after which Frodo walked off and he (Boromir) had wandered the forest for a time. Not entirely believing all Boromir had related, the Fellowship split up and searched the forest for Frodo.
During this search, the Fellowship was ambushed by orcs and Uruk-Hai from Isengard. Boromir valiantly attemped to protect Merry and Pippin from the Uruk-Hai, but after receiving many arrow wounds (three in the film version of FotR), Boromir could fight no longer and the hobbits were taken.
Aragorn, having heard the blast of Boromir's horn, attempted to come to Boromir's aid, but came too late to prevent the hobbit's capture. As Boromir lay dying, he urged Aragorn to save Minas Tirith, believing that he himself had failed in that task. Aragorn reassured him that he had not failed, that "few have gained such a victory". Aragorn, Gimli, and Legolas placed Boromir's body in one of the Elven boats, along with his sword, belt, cloak, broken horn, and the weapons of his slain foes. They set the boat adrift in the river toward the Falls of Rauros, and sang a "Lament of the Winds" as his funeral song.
"Through Rohan over fen and field where the long grass grows, The West wind comes walking, and about the walls it goes. 'What news from the west, O wandering wind, do you bring to me tonight? Have you seen Boromir the Tall by moon or by starlight? 'I saw him ride over seven streams, over waters wide and grey; I saw him walk in empty lands, until he passed away, Into the shadows of the North. I saw him then no more. The North Wind may have heard the horn of the son of Denethor.' 'O Boromir! From the high walls westward I looked afar, But you come not from the empty lands where no men are."
* * * * *
Boromir is a perfect example of a Knight In Battered Armor. He fights for his friends and comrades in arms. The 'battered' part comes from when he tried to force Frodo to give up the One Ring, and then attempted to steal it when Frodo refused to hand it over. He later redeemed himself by fighting the Uruk-Hai that ambushed Merry and Pippin. And even though he was wounded by arrows, he continued to fight until there was no more fight in him. He tooks hit; he was wounded, yet still fought on regardless of the outcome. He chose to fight despite overwhelming odds.
Truly, he is a Knight In Battered Armor.