Ramon Casas i Carbó (Catalan pronunciation: [rəˈmoŋ ˈkazəs]; 4 January 1866 – 29 February 1932) was a Catalan artist from Spain. Living through a turbulent time in the history of his native Barcelona, Catalonia, he was known as a portraitist, sketching and painting the intellectual, economic, and political elite of Barcelona, Paris, Madrid, and beyond. He was also known for his paintings of crowd scenes ranging from the audience at a bullfight to the assembly for an execution to rioters in the Barcelona streets (El garrot). Also a graphic designer, his posters and postcards helped to define the Catalan art movement known as modernisme.

Casas was born in Barcelona. His father had made a fortune in Matanzas, Cuba; his mother was from a well-off Spanish family. In 1877 he abandoned the regular course of schooling to study art in the studio of Joan Vicens. In 1881, still in his teens, he was a co-founder of the magazine L'Avenç; the 9 October 1881 issue included his sketch of the cloister of Sant Benet in Bages. That same month, accompanied by his cousin Miquel Carbó i Carbó, a medical student, he began his first stay in Paris, where he studied that winter at the Carolus Duran Academy and later at the Gervex Academy, and functioned as a Paris correspondent for L'Avenç. The next year he had a piece exhibited in Barcelona at the Sala Parés, and in 1883 in Paris the Salon des Champs Elysées exhibited his portrait of himself dressed as a flamenco dancer; the piece won him an invitation as a member of the salon of the Societé d'artistes françaises.

The next few years he continued to paint and travel, spending most autumns and winters in Paris and the rest of the year in Spain, mostly in Barcelona but also in Madrid and Granada; his 1886 painting of the crowd at the Madrid bullfighting ring was to be the first of many highly detailed paintings of crowds. That year he survived tuberculosis, and convalesced for the winter in Barcelona. Among the artists he met in this period of his life, and who influenced him, were Laureà Barrau, Santiago Rusiñol, Eugène Carrière, Pierre Puvis de Chavannes, and Ignacio Zuloaga.

Casas and Rusiñol traveled through Catalonia in 1889, and collaborated on a short book Por Cataluña (desde mi carro), with text by Rusiñol and illustrations by Casas. Returning together to Paris, they lived together at the Moulin de la Galette in Montmartre, along with painter and art critic Miquel Utrillo and the sketch artist Ramon Canudas. Rusiñol chronicled these times in as series of articles "Desde el Molino" ("From the Mill") for La Vanguardia; again Casas illustrated. Casas became an associate of the Societé d'artistes françaises, allowing him to exhibit two works annually at their salon without having to pass through jury competition.

With Rusiñol and with sculptor Enric Clarasó he exhibited at Sala Parés in 1890; his work from this period, such as Plen Air and the Bal du Moulin de la Galette lies somewhere between an academic style and that of the French Impressionists. The style that would become known as modernisme had not yet fully come together, but the key people were beginning to know one another, and successful Spanish artists were increasingly coming to identify themselves with Barcelona as much as with Paris.

His fame continued to spread through Europe and beyond as he exhibited successfully in Madrid (1892, 1894), Berlin (1891, 1896) and at the World Columbian Exposition in Chicago (1893); meanwhile the bohemian circle that included Casas and Rusiñol began with greater frequency to organize exhibitions of their own in Barcelona and Sitges. With this increasing activity in Spain, he settled more in Barcelona, but continued to travel to Paris for the annual Salons.

The emerging modernista art world gained a center with the opening of Els Quatre Gats, a bar modeled on Le Chat Noir in Paris. Casas largely financed this bar on the ground floor of Casa Martí, a building by Architect Josep Puig i Cadafalch in Montsió Street near the center of Barcelona; it opened in June 1897 and lasted for six years (and was later reconstructed in 1978). His partners in the enterprise were Pere Romeu, who largely played host to the bar, as well as Rusiñol and Miquel Utrillo.

The bar hosted tertulias and revolving art exhibits, including one of the first one-man shows by Pablo Picasso; the most prominent piece in its permanent collection was a lighthearted Casas self-portrait, depicting him smoking a pipe while pedaling a tandem bicycle with Romeu as his stoker. The original of the painting—or most of it: nearly a third of the canvas was cut away by an intervening owner—is now in Barcelona's Museu Nacional d'Art de Catalunya (MNAC); a creditable reproduction resides in the revived Els Quatre Gats.