Klashorst was born in Santpoort and graduated cum laude from the Gerrit Rietveld Academie in Amsterdam in the early nineteen eighties. During this period a new art movement arose in Europe, namely “The New Wild Ones”. Klashorst became one of its leading personalities. In 1983 he received a prestigious Dutch Royal award (Koninklijke Subsidie voor de Vrije Schilderkunst) from Queen Beatrix.
In 1987 Klashorst was one of the initiators of “After Nature”, an international art collective that aimed at reinventing painting and bringing art back to society and taking it out of the official highbrow art world. Famous and notorious for their joint performances on streets and in nightclubs, they toured the world and were a notorious phenomenon of their time. The collective “After Nature”, including co-founders Klashorst and the artists Roberto Cabot, George Dokoupil, Donker brothers and Ernst Voss, opposed the prevailing non-figurative style and was interested in just painting what they saw.