Who is Brownie from The Man Who Listens to Horses and what is their importance?

Brownie was Monty's favorite horse when he was a child. His father scared Brownie with paper (disciplinary tactic) when he was young, and as a result, Brownie was afraid of paper his entire life. When Brownie dies, Monty's father helped bury him, something Monty says was the kindest gesture his father ever made.