Romain de Tirtoff, known by the pseudonym Erté, was a Russian-born French artist, fashion designer, and set designer, whose illustrations graced more than 200 Harper's Bazaar covers between 1915 and 1937. He is best known for capturing the Art Deco style with his elongated, elegant figures and their intricate outfits, which he continued to create through the 1980s.
Images 1-6, 8, and 16 via The Coincidental Dandy.
Images 10-11 via Erte.com.
Images 7, 9, 12-15 via KingPaper.
Image 17 via stmarygypsy.
Image 18 via theflappers.
Image 19 via thelateness.