Mary Lou Williams (born Mary Elfrieda Scruggs; May 8, 1910 – May 28, 1981) was an American jazz pianist, arranger, and composer. She wrote hundreds of compositions and arrangements and recorded more than one hundred records (in 78, 45, and LP versions). Williams wrote and arranged for Duke Ellington and Benny Goodman, and she was friend, mentor, and teacher to Thelonious Monk, Charlie Parker, Miles Davis, Tadd Dameron, Bud Powell, and Dizzy Gillespie.

The second of eleven children, Williams was born in Atlanta, Georgia, and grew up in the East Liberty neighborhood of Pittsburgh, Pennsylvania. A musical prodigy, at the age of three, she taught herself to play the piano. Mary Lou Williams played piano out of necessity at a very young age; her white neighbors were throwing bricks into her house until Williams began playing the piano in their homes. At the age of six, she supported her ten half-brothers and sisters by playing at parties. She began performing publicly at the age of seven when she became known admiringly in Pittsburgh as “The Little Piano Girl”. She became a professional musician at the age of 15, citing Lovie Austin as her greatest influence. She married jazz saxophonist John Williams in November 1926.