Fats Waller was an American jazz pianist, organist, composer, singer, and comedic entertainer. He was one of the most popular performers of the 1920s and 1930s, and his influence on jazz music and popular culture was immense. His signature song was 'Ain't Misbehavin', ' and he was also known for his rendition of 'The Joint is Jumpin'.' Waller's nickname was 'The King of the Keys, ' and he was also known as 'Fats' due to his large size. The term 'domino or waller' refers to Waller's style of playing the piano, which was characterized by a steady rhythm and a syncopated left hand.