Mary Lou Williams (May 8, 1910 – May 28, 1981) was an American jazz pianist, composer, and arranger. She was born Mary Elfrieda Scruggs in Atlanta, Georgia and grew up in Pittsburgh, Pennsylvania. As a very young child she taught herself to play the piano (her first public performance was at the age of six). She became a professional musician in her teens. In 1930, she joined Andy Kirk's Twelve Clouds of Joy, of which her first husband, saxophonist John Williams, was already a member, and became the band's leading soloist, composer, and arranger.

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