Complex sentence: She was the first to record Leiber and Stoller's "Hound Dog", in 1952, which became her biggest hit, staying seven weeks at number one on the "Billboard" R&B chart in 1953 and selling almost two million copies.
Split into simpler sentences: She was the first to record Leiber and Stoller's "Hound Dog", in 1952, which became her biggest hit. It spent seven weeks at number one on the "Billboard" R&B chart in 1953 and sold almost two million copies.