Balin & Dwalin

Balin is a wise and kind dwarf, a friend of Bilbo. Some of his character traits:
He survived difficult times and took part in many battles.
Doubts the wisdom of trying to retake the Lonely Mountain.
In Thorin's company, Balin "acted as a lookout": he waited for Bilbo at the door of the Green Dragon inn, was the first to notice the fire lit by the trolls in the forest, and was the first to see the elves in Mirkwood.
After escaping from the goblins in the Misty Mountains, Balin, being the company's lookout, did not notice Bilbo (who had put on a magic ring and became invisible), after which he began to respect the hobbit as a "burglar".

Dwalin is one of the company's most steadfast warriors. Some of his character traits:
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A strong and resilient fighter, not one to be easily defied.
A tendency to distrust anyone who is not a dwarf, especially anyone who might be an elf.
When the company set out on a journey, it was Dwalin who lent his cap and cloak to the unprepared Bilbo.

Interaction: Balin and Dwalin usually work together. For example, during the Warg attack, they perched together in the same tree, a tall, slender spruce. Also, during their introduction to Beorn, they appeared before him together, as the third pair.