Thelonious Monk was born October 10, 1917, in Rocky Mount, North Carolina, the son of Thelonious and Barbara Monk, two years after his sister Marion. A brother, Thomas, was born in January 1920. In 1922, the family moved to 243 West 63rd Street, in Manhattan, New York City. Monk started playing the piano at the age of six. Although largely self-taught, he did study music theory, harmony and arranging at the Juilliard School of Music. Monk attended Stuyvesant High School, but did not graduate. He toured with an evangelist in his teens, playing the church organ, and in his late teens he began to find work playing jazz.
In the early to mid-1940s, Monk was the house pianist at Minton's Playhouse, a Manhattan nightclub. Much of Monk's style was developed during his time at Minton's, when he participated in after-hours "cutting competitions" which featured many leading jazz soloists of the time. The Minton's scene was crucial in the formulation of bebop and it brought Monk into close contact with other leading exponents of the emerging idiom, including Dizzy Gillespie, Charlie Christian, Kenny Clarke, Charlie Parker and, later, Miles Davis. Monk is believed to be the pianist featured on recordings Jerry Newman made around 1941 at the club. Monk's style at this time was later described as "hard-swinging," with the addition of runs in the style of Art Tatum. Monk's stated influences included Duke Ellington, James P. Johnson, and other early stride pianists. In the documentary Thelonious Monk: Straight, No Chaser, it is stated that Monk lived in the same neighborhood in New York City as Johnson and knew him as a teenager.
Mary Lou Williams, who acted as a mentor to Monk and his compatriots, spoke of Monk's rich inventiveness in this period, and how such invention was vital for musicians since at the time it was common for fellow musicians to incorporate overheard musical ideas into their own works without giving due credit. "So, the boppers worked out a music that was hard to steal. I'll say this for the 'leeches', though: they tried. I've seen them in Minton's busily writing on their shirt cuffs or scribbling on the tablecloth. And even our own guys, I'm afraid, did not give Monk the credit he had coming. Why, they even stole his idea of the beret and bop glasses.