N°19 was created by Henri Robert and owes its name to 19 August, Gabrielle Chanel's birthday. Chanel's history dates its launch to 1970, shortly before her death at the Ritz on 10 January 1971; Wikipedia gives the first marketing as 1971.
The house describes it as a green floral whose main note is iris, giving it a powdery touch. Wikipedia lists galbanum, neroli, bergamot, jasmine, rose, lily of the valley, iris, vetiver, sandalwood, leather and musk, and notes that the galbanum and leather make it hard to classify: some call it a green floral, others a chypre.
In the 1970s and 1980s it was advertised as "The Unexpected Chanel" and "The Outspoken Chanel". Jacques Polge later created a softer flanker, N°19 Poudré, in 2011.