Danish painter whose large, colouristic compositions of the 1930s were the first important abstract (abstract art) works in Danish art.

Mortensen studied at the Royal Academy of Art in Copenhagen but left after two years to work independently. In 1932 he first saw Wassily Kandinsky (Kandinsky, Wassily)'s paintings in Berlin, which influenced him to introduce abstraction into his own work. He was also interested in the work of Surrealist (Surrealism) artists such as Salvador Dalí (Dalí, Salvador), and in the mid-1930s he combined abstract compositions with incongruous, naturalistically painted elements. In Copenhagen he founded the Linien (“The Line”) group of abstract painters.

Mortensen's paintings became increasingly expressive and violent during World War II. In 1947 he moved to Paris, where he painted in a purely abstract style. Mortensen remained committed to geometric abstraction, conveying through vivid colour and lively rhythm a sense of spontaneity within hard-edged structure. He also designed tapestries and stage settings.