Who is Roac and why is he important to the dwarves in The Hobbit?please help!

In chapter fifteen, "The Gathering of the Clouds," Bilbo
and the dwarves wonder what has been happening and where is Smaug.  They had kept watch
all night long and in the morning, Bilbo notices that many birds have been flying past
the mountain.  The old thrush reappears and unsuccessfully tries to tell the dwarves
something.   Balin wishes aloud for a raven, because "there used to be great friendship
between them and the people of Thror" (231).  Before Smaug, a famous pair of ravens,
Carc and his wife, lived above the guard chamber, often bringing the dwarves secret
news.

Later, the old thrush returns to the dwarves with a
raven, "a most decrepit old bird.  He was getting blind, he could hardly fly, and the
top of his head was bald" (231).  This raven is Roac, son of Carc, and chief of the
great ravens of the Mountain.  Roac "remember[s] still the king that was of old" (231). 
Roac brings the dwarves glad tidings, that Smaug is dead, but he also warns Thorin that
lake-men's town has been destroyed and they will be wishing for amends from the dwarves'
treasure.  Lastly, the old raven offers Thorin some sage advice--he should "not trust
the Master of the Lake-men, but rather him that shot the dragon with his bow" (232). 
The raven believes that Thorin should make a deal with Bard and restore peace to the
valley. 

Thorin, of course, is not interested in parting
with his treasure whatsoever. Needing some back up for the looming fight ahead, Thorin
instructs Roac to send flyers to his cousin Dain in the Iron Hills for help.