Théo (Théophile) van Rysselberghe (Gent, 23 november 1862 - Le Lavandou, 14 december 1926) was een Belgische neo-impressionistische kunstschilder, graficus en ontwerper, die op het einde van de 19de eeuw een sleutelrol speelde binnen de Europese kunstwereld. Zo was hij onder meer een van de oprichters van de avant-gardegroep Les Vingt in 1883.
Yet his next portraits are in rather subdued colours, using different black or purple gradations contrasting with light colours: Jeanne and Marguerite Schlobach (1884), Octave Maus (1885), Camille Van Mons (1886), Marguerite Van Mons (1886) (to be compared with Portrait of Gabrielle Braun (1886) by Fernand Khnopff).
He saw the works of the impressionists Monet and Auguste Renoir at the show of Les XX in 1886. He was deeply impressed. He experimented with this technique, as can be seen in Woman with Japanese album (1886). This impressionist influence became prominent in his paintings Madame Picard in her Loge (1886) and Madame Oscar Ghysbrecht (1886) (painted in a palette of bright colours). In 1887 he painted some impressionist seascapes at the Belgian coast : Het Zwin at high tide (1887)
Because of his growing ties with the Parisian art scene, Octave Maus sent him as a talent scout to Paris to look out for new talent for the next exhibitions of Les XX.
He discovered the pointillist technique when he saw Georges Seurat's La Grande Jatte at the eighth impressionist exhibition in Paris in 1886. This shook him up completely. Together with Henry Van de Velde, Georges Lemmen, Xavier Mellery, Willy Schlobach and Alfred William Finch and Anna Boch he "imported" this style to Belgium. Seurat was invited to the next salon of Les XX in Brussels in 1887. But there his La Grande Jatte was heavily criticized by the art critics as "incomprehensible gibberish applied to the noble art of painting".
Théo van Rysselberghe abandoned realism and became an adept of pointillism. This brought him sometimes in heavy conflict with James Ensor. In 1887 van Rysselberghe already experimented with this style, as can be seen in his Madame Oscar Ghysbrecht (1887) and Madame Edmond Picard (1887). While staying in summer 1887 a few weeks with Eugène Boch (brother of Anna Boch) in Batignolles, near Paris, he met several painters from the Parisian scene such as Sisley, Signac, Degas and especially Henri de Toulouse-Lautrec. He appreciated especially the talent of Toulouse-Lautrec. His portrait Pierre-Marie Olin (1887) closely resembles the style of Toulouse-Lautrec of that time. He managed to invite several of them, including Signac, Forain, and Toulouse-Lautrec to the next exhibition of Les XX.