Who is Roonwit the Centaur from The Last Battle and what is their importance?

Roonwit the Centaur is a reader of the stars. He goes to Tirian to tell him the truth about Aslan, and when a dryad appears with the news about Lantern Waste, Roonwit questions the King's wrath and is sent to gather men and beasts to help. Although Roonwit is killed, he is able to pass on a message to Farsight the Eagle before he dies.