For me, it is the music of the soul that somes from the heart. You know it from how it is sung and played (through instruments like guitar, piano, sax etc.). The history took us way back to the era in which the blacks worked as slaves. While working in cotton fields they used to sing or chant in a manner of showing their deepest sorrow and depression.
Through the years the chant was developed and improvised through the used of musical instruments such as the guitar and piano. Later, the music was commercialized.
Some of the most influential blues men in the early years are Robert Johnson, BB King, Buddy Guy and Muddy Waters.