Who is Padre Agostino of San Marco from Padre Pio: The True Story and what is their importance?

Padre Agostino was Pio's closest friend throughout his lifetime. They lived in the same friary, and Agostino was eventually assigned to look out for Pio and watch over him during his spiritual trials and future fame. Agostino also made detailed records of Pio's conversations and ecstasies.