Amos Leon Thomas Jr. (October 4, 1937 – May 8, 1999), known professionally as Leon Thomas, was an American jazz and blues vocalist, born in East St. Louis, Illinois, and known for his bellowing glottal-stop style of free jazz singing in the late 1960s and 1970s.

Leon Thomas was born Amos Thomas, Jr. on October 4, 1937, in East St. Louis, Illinois. He studied music at Tennessee State University. At the time of his studies, he had begun a singing career as a guest vocalist for the jazz bands of percussionist Armando Peraza, saxophonist Jimmy Forrest, and guitarist Grant Green. His musical development at this time was shaped in part by seeing saxophonist John Coltrane perform in trumpeter Miles Davis‘s sextet during the late 1950s. Thomas moved to New York City in 1959, singing at the Apollo Theater as a vocalist for acts such as jazz ensemble The Jazz Messengers and singer Dakota Staton. In 1961, he joined the Count Basie Orchestra but soon left after being conscripted into the army.