The style of naive painting is characterized by a careful, simplifying approach, non-scientific perspective, bright colors, and often, an enchantingly literal depiction of imaginary scenes. Although not following any particular movement or aesthetic, naive painters have been a continuing international phenomenon and influence since the beginning ot the twentieth century. The term usually refers to works produced by artists (also called naifs or na?fs) who had no formal training. Some trained artists, however, have deliberately affected a naive style. Among the artists whose work may be called naive, Henri Rousseau (French, 1844-1910) is the most famous. His nickname, "Le Douanier," refers to his employment as a toll-collector when he took up painting as a spare-time occupation. Rousseau's simplicity and naivety were notorious, his paintings childlike, non-naturalistic, and brightly colored. His pictures are appealing in their directness and depth, and in some ways are very sophisticated, their design and colors worked out in great detail. Their apparent affinity with non-Western art and their bold expressive qualities made them appealing to the early modernists searching for new forms of expression.