Milman Parry was an influential American scholar who studied the oral tradition of epic poetry in the early 20th century. He is best known for his work on the oral-formulaic nature of storytelling, particularly in ancient texts like the 'Iliad' and 'Odyssey'. Parry's theories changed the understanding of how oral traditions function and how they relate to the composition of epic poetry, revealing that these works were often created through repeated formulas and patterns instead of being meticulously crafted in written form.