artist who painted some of the earliest Japanese suiboku works—a Chinese-inspired style of monochromatic ink painting favoured by Zen Buddhist priest-painters. His portrait of Kanzan, a mythical figure who represents the Zen way of life, and the techniques used in the portrait (strong abbreviated outlines that contrast with soft washes, asymmetrical composition, and significant empty space) foreshadow those of the suiboku school, which flourished in the 15th and 16th centuries.

There has been much confusion about the identity of Kaō, whose name appears on the portrait of Kanzan and on other early suiboku-ga. Some believe that Kaō was a high-ranking Zen priest named Kaō Sōnen; others have identified him as the painter Ryōzen, though the latter suggestion has been largely discounted on stylistic grounds. Still others have suggested that he was another professional Buddhist painter associated with the Takuma school. Whatever Kaō's true identity, his work, along with that of Mokuan, a Japanese priest-painter of the early 14th century, constitutes the foundation of ink painting in Japan.