Who is Marvin Earl Roberts from The Man Who Listens to Horses and what is their importance?

Marvin Earl Roberts is Monty's father. Throughout his life, Monty has a negative relationship with his father. When Monty is a child, his father trains horses for clients, operates a riding school, and leases the facility to horse trainers. However, Marvin is violent and harsh in his treatment of the horses. Marvin acquaints Monty with horses at an early age. In fact, he instructs Monty to mistreat the horses as well. Monty refuses to use any sort of violence on horses. As a result, Marvin ends up resenting him even more. Throughout Monty's childhood, Marvin abuses him physically. In fact, he leaves him hospitalized on several occasions. Additionally, Marvin gets his son jobs as a stunt double in Hollywood movies. While this work is dangerous, Marvin requires his son to do this work without any complaint. Marvin also spends the money that Monty earns as a stunt double, while lying and telling Monty that he is saving it for him.