Appel was a protagonist of the avant-garde movement Cobra. His work explored classical themes: the figure, the animal, landscape and their combinations. However, his creative idiom differed from the classical approach. Experimentation with colour enabled him to control it. “By means of colour I can now do what I want. Yet, it is always a struggle”, as he put it. Gradually, he departed from figuration, executing his paintings in thick impasto and violent colours, creating eruptive forms. His artistic expression showed affinity with Art Brut and involved a spontaneous expressive and emotional process characteristic of immediacy and an unrestrained treatment of the medium. He pressed paint from the tube directly on to the canvas, shaping thick layers with a spatula. This was logically linked to the abstraction of the motif. Appel’s painting oscillated quite naturally between figuration and abstraction and their mutual penetration. The series of female nudes, transformations of landscape or cosmological compositions on the theme of the Almighty were created at about the same time. Appel used calligraphic, linear and drip painting, screens and spirals, blending the vocabulary of Art Informel and Postmodernism. Rejecting the classical and the traditional, he intensified inspirations drawn from 20th century avant-gardes to create an original artistic expression.