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

Brownie is Monty's favorite childhood horse. Monty's father scares Brownie with paper by disciplining him with it when he is young. As a result, Brownie is scared of paper throughout his whole life. He helps Monty win numerous competitions during Monty's teens. When Brownie dies, Monty's father helps him to bury him. Monty says that this is the kindest gesture that his father has ever made.