Blues is the sorrowful music based on 'blue notes' which developed from the work songs and chants of African American slaves. Commonly built on 8, 12 or 16-bar patterns, the Blues musician usually tells simple narratives in a ballad style, usually about romantic worries or everyday problems. Important Blues musicians include Muddy Waters, Howlin' Wolf, Robert Johnson and BB King.The Blues were the bedrock of Rock n' Roll, with songs like "Hound Dog", "Shake Rattle and Roll" and "Tutti Frutti" all being based on basic blues patterns. While Rock quickly grew arms and legs of its own, often unrelated to the Blues, others like Led Zeppelin and Cream continued to show heavy Blues influences.