Final answer:
Buddy Holly's song "That'll Be the Day" is often considered one of his most iconic hits, representing his important contribution to the rock and roll genre during his brief but significant career.
Step-by-step explanation:
Among Buddy Holly's most iconic hits, the song "That'll Be the Day" is often celebrated as a quintessential track that exemplifies his significant impact on the rock and roll genre. The song showcases Holly's idiosyncratic vocal style and innovative musical approach, blending elements of rockabilly with early rock and roll. Despite the breadth of Holly's influential and enduring body of work, "That'll Be the Day" stands out as particularly emblematic of his contribution to music and the development of the genre.