Louis Couperin (c1626-1661) was a French Baroque composer and performer. He was born in Chaumes-en-Brie and moved to Paris in 1650–1651 with the help of Jacques Champion de Chambonnières. Couperin worked as organist of the Church of St. Gervais in Paris and as musician at the court. He quickly became one of the most prominent Parisian musicians, establishing himself as a harpsichordist, organist, and violist, but his career was cut short by his early death at the age of thirty-five.
None of Couperin's music was published during his lifetime, but manuscript copies of some 200 pieces survive, some of them only rediscovered in the mid-20th century. The first historically important member of the Couperin family, Couperin made contributions to the development of both the French organ school and the French harpsichord school. His innovations included composing organ pieces for specific registrations and inventing the genre of the unmeasured prelude for harpsichord, for which he devised a special type of notation.
Unmeasured or non-measured prelude is a prelude in which the duration of each note is left to the performer. The first unmeasured preludes appeared during the Renaissance era. They were short improvised compositions for lute, usually performed as an introduction to another piece of music or to test the instrument. Later unmeasured lute preludes retained the improvisatory character of the genre but became more complex and lengthy. Unmeasured preludes flourished into full-fledged compositions by the middle of the 17th century. Unmeasured preludes for harpsichord started appearing around 1650. Louis Couperin is usually credited as the first composer to embrace the genre. Couperin wrote unmeasured preludes using long groups of whole notes, and these groups were connected by long curves. The first ever published unmeasured preludes appeared in Lebègue's Les pieces de clavessin in 1677.