Balin was a Dwarf leader, the son of Fundin and elder brother of Dwalin. Balin was among the Dwarves that travelled with Bilbo Baggins and Gandalf in The Hobbit.
Among the Dwarves in The Hobbit, Balin was the second-eldest Dwarf on the quest (behind Thorin), and so he spoke for the party when they were captured by the Elvenking.
He is described as "always their look-out man": He spots Bilbo approaching the Green Dragon Inn at Bywater, he spots the trolls' fire, and he's the first to spot the Elves in Mirkwood.
Conversely he did not notice Bilbo (hidden by wearing the magic ring) as look-out for the company after escaping the Goblins in the Misty Mountains. After this bit of trickery Balin gained respect for Bilbo's abilities. He's the only Dwarf that volunteers to accompany Bilbo down the secret passage to Smaug. Of all the Dwarves in the quest, he's the only one known to have visited Bilbo afterwards at Bag End.
In 2989 T.A. Balin left Erebor and entered Moria with Flói, Óin, Ori, Frár, Lóni and Náli. He was slain by an Orc archer in Dimrill Dale in 2994 T.A.
In The Lord of the Rings, the Fellowship of the Ring discovers his tomb in the Chamber of Mazarbul.