Sigmar Polke was one of the most significant German artists to emerge in the 1960s, making art in a huge range of materials from painting, drawing and film to potatoes, snail juice and meteor dust. As an artist he responded to consumer society, confronted the memory of the Nazi's, and took hallucinogenic drugs. In this TateShots, curator Mark Godfrey explains why he thinks Polke is "one of the most exciting and experimental artists of the last 50 years.