It is not possible to overstate the influence of Paul Cézanne on 20th-century art. He’s the modern Giotto, someone who shattered one kind of picture-making and invented a new one that the world followed. Matisse called Cézanne “a sort of God”; Picasso said he was “the father of us all.” Max Beckmann called him “the last old master. . . the first new master.” He’s also an artist who can be hard to come to terms with: Great art often looks ugly when first seen, and Cézanne’s is an extreme case, so much so that his work can still vex. His optical disequilibrium made peers dubious, friends skeptical and critics jeer.