Theo van Doesburg (born Christian Emil Marie Küpper) (August 30, 1883 – March 7, 1931) came in the hierarchy of de stijl movement second only to Piet Mondrian.

As Mondrian did not have directed duties in publicizing affairs concerning the movement, Doesburg assumed this task and moved to Weimar in 1922, deciding to make an impression on the Bauhaus principal, Walter Gropius, in order to spread the influence of de stijl.

Although Gropius accepted a turn towards constructivism in 1923, he did not feel that Doesburg could become a Bauhaus master. Doesburg then installed himself near to the Bauhaus buildings and started to attract school students interested in the new ideas of constructivism. Later on, Doesburg would split with his master, Mondrian, because of divergent ideas about the directions of the lines in the square scheme of de stijl paintings. Mondrian never accepted diagonals, whereas Doesburg insisted on the diagonal's dynamic aspects, and indeed featured it in many of his works. However, Mondrian accepted some concepts of diagonals, such as in his "Lozenge" paintings, where the canvas was rotated 45 degrees, while still maintaining horizontal lines. This effect gave the impression of lines extending beyond the canvas while maintaining the horizontal characteristic Mondrian stuck to.

Apart from his design activities, which even included architecture (Houses for artists, together with Georges Vantongerloo , the designs for the decoration of Café Aubette), Doesburg also kept a link with DADA poetry, publishing the magazine DADA Holland under the false name of "I. K. Bonset". Together with El Lissitzky and Kurt Schwitters, Doesburg pioneered the efforts to an International of Arts in two congresses held in Düsseldorf and Weimar, still in 1922.

He died in France in 1931, after another international effort under the group Cercle et carré.