Sonderborg studerte ved Atelier 17, St. W. Hayter i Paris. Han arbeidet deretter i London, Cornwall, New York, Ascona, Roma og Paris.
Sonderborg har blant annet deltatt ved Saõ Paolo Biennalen.

1923 - 2008.

The Danish painter K.R.H. Sonderborg - actually Kurt Rudolf Hoffmann - is born in Sonderborg on April 5, 1923. The family moves to Germany the same year. As of 1951 the artist Rudolf Hoffmann calls himself K.R.H. Sonderborg after his home town.

He goes to school in Hamburg and does a merchant's apprenticeship as of 1939. He is a private student of the painter Ewald Becker-Carus in Hamburg in 1946. From 1947 to 1949 he studies painting, graphic art and textile design at the State Art School in Hamburg under Willem Grimm and Maria May. He joins the artists group "ZEN 49" in 1953. He goes to Paris the same year where he receives training in engraving from Stanley William Hayter in the Atelier 17. Paris is also the place where he first encounters Tachism. In the following the artist goes on longer journeys and works for some time in London, Cornwall, New York, Ascona, Rome and Paris again. In New York K.R.H. Sonderborg comes into contact with Action Painting.

His own style is becoming abstract, painting in swift broads strokes, that reveal the painting process, with spontaneous color application. Black and white contrasts are an important feature, later he adds colors such as cadmium red.

K.R.H. Sonderborg takes part in the 1958 Biennale in Venice. He is awarded the Prize for Graphic Art at the Biennale in Tokyo in 1960 as well as the Great International Prize for Drawing at the 1963 Biennale in São Paulo. The artist shows works at the documenta in Kassel in both 1959 and 1964. From 1965 to 1990 he holds a post as professor for painting at the Stuttgart Art Academy. In 1969/70 he is guest lecturer at the Minneapolis College of Art and Design, as well as at the Art Institute in Chicago in 1986.

Along with artists such as Karl Otto Götz, Gerhard Hoehme, Bernhard Schulze, Peter Brüning etc., K.R.H. Sonderborg belongs to the most important and most impressive representatives of German Informal Art.

K.R.H. Sonderborg dies in Hamburg on February 19, 2008.