Ay-O (bürg. Takao Iijima, b. 1931) is a Japanese artist who also became known as the "Rainbow Man" and has been part of the international Fluxus movement since the 1960s. He worked closely with Fluxus artists George Maciunas, Emmett Williams, Dick Higgins and Nam June Paik, developing performances and designing his Finger Boxes, which have become famous. In Japan in particular, but also in the U.S. and Europe, he raised the profile of Fluxus through striking and aesthetically pleasing paintings such as his portraits and still lifes painted in rule-bow-like gradations of color. He also continued the concept of rainbow colors in happenings and installations, creating a new, aesthetic form of abstraction from everyday objects.
Ay-O related his artistic work to Japanese mythology and carried elements from it into contemporary art through abstraction. He was part of the Democrato Artist Association and Sōzō Biiku, influential artist organizations in Japan, and participated in the 1966 Venice Biennale and the 1971 São Paulo Biennale.