Which Czech artist created iconic Art Nouveau posters of Sarah Bernhardt?

The Czech artist who created iconic Art Nouveau posters of Sarah Bernhardt was Alphonse Mucha.

Born in 1860 in Moravia, then part of the Austrian Empire and now the Czech Republic, Mucha built his reputation in Paris. His breakthrough came in December 1894, when he was asked at short notice to design a poster for Gismonda, a play starring the celebrated French actress Sarah Bernhardt. The unusually tall poster showed Bernhardt in costume beneath an arched, halo-like motif.

Bernhardt was impressed and signed Mucha to a five-year contract. He subsequently designed posters for her productions of La Dame aux Camélias, Lorenzaccio, Medea, La Tosca, and Hamlet, as well as theatrical programs, costumes, sets, and jewelry. His flowing hair, floral ornament, elongated figures, and decorative lettering became a defining visual language of French Art Nouveau.

Mucha was Czech, but his Bernhardt posters were produced during his Paris career. Toulouse-Lautrec was also a major poster artist, while Klimt belonged chiefly to the Vienna Secession; neither created this celebrated Bernhardt series.