The story of Balin is told in Malory's Morte d'Arthur, with Malory calling him "Balin Le Savage". Balin and Balan are the tragic brothers who are destined to eventually end up killing each other in battle.
Balin leads a life cursed with misfortune. A knight whom he is protecting is killed by the treacherous, invisible, knight Garlon. When Balin attempts to avenge the death by tracking Garlon down to the castle of King Pellam, he gets involved in a fight, lashes out in self defence and wounds the lord of the castle, King Pellam, with the sacred spear that pierced the side of Christ. This blow is the Dolorous Stroke, which lays the waste the land and produces a wound that can only be healed when the Grail is achieved eventually by Sir Galahad.
In Malory's version of the story, Balin wins a second sword through chivalry, and becomes known as The Knight with Two Swords. He is warned that if he keeps both swords, then he will kill the man he loves most in the world and bring about his own destruction. By disbelieving this prophecy and keeping both swords, the fate of his brother and himself is sealed. He fails to recognise his brother in battle and kills him.
Tennyson makes Balin an important figure. His Balin is known as "the Savage". Published in 1885 in the volume Tiresias and Other Poems, the "Balin and Balan" idyll was the last to be written.
Swinburne also retold the story of Balin in his The Tale of Balin, which follows Malory much more closely than Tennyson's version.
Full references to more about Balin at the Rochester site
Sir Balin and Sir Balan are two of the many clourful characters who appear in the legends of King Arthur.
Characters from King Arthur's legends