Who is Fast Horse from Fools Crow and what is their importance?

Fast Horse is a youth one year younger than White Man's Dog who stands a head taller than his friend. He carries himself erectly with a stance of pride that borders on arrogance. He wears his hair in a knot on the front of his head. At the start of the story he is a braggart and thinks himself quite important because he will inherit the same medicine his father acquired.