His technique involved applying paint in small, distinct patches that resemble a mosaic. He studied under Hans Hofmann but eventually rejected the strict rules of abstract expressionism. His work often features flat, bold shapes and heavy outlines. In pieces like Emperor Maximilian I, he looks back to Northern Renaissance history and folklore. He used a palette of earthy tones and stark whites to create images that feel ancient.

Modern collectors value Müller for his ability to bridge the gap between traditional history painting and modern expressionism. His prints offer a sense of weight and history without the clutter of classical realism. The bold silhouettes and structured compositions provide a strong visual presence in a room. His work appeals to those who appreciate the energy of the mid-century New York art scene but prefer a subject with narrative roots.