Ay-O, born Takao Iijima in 1931 in Ibaraki. He once lived in Taiwan during the Japanese occupation period with his father, who was serving in the navy. Ay-O moved to New York in 1958 and did not return to Japan until the early 2000s. At that time, New York was the hub leading global art movements. While abstract painting was highly dominant, Ay-O sought to break free from the framework of this style, searching for his own artistic language. Through the introduction of Yoko Ono (1933–), Ay-O became one of the few Asian artists involved in the Fluxus movement, which helped him solidify his creative focus on blending sensory experiences with art.

Fluxus, an international avant-garde art movement that emerged in the 1960s, was characterized by a strong spirit of rebellion. Its members included artists, musicians, writers, and dancers from around the world, breaking down the boundaries between different artistic disciplines. Led by key figure George Maciunas (1931–1978), they emphasized the democratization and inclusiveness of art, believing that anyone could participate. They aimed to merge art with everyday life through various creative media and approaches, expanding the boundaries of art. Like other Fluxus members who often collaborated to spark new ideas, the active Ay-O had a close relationship with Nam June Paik (1932–2006), the father of Korean video art. The two were neighbors for many years and influenced each other in their artistic creations.

In 1962, the rainbow appeared in Ay-O's oil painting for the first time and has since become the core concept of his art. Drawing from scientific principles, he abandoned traditional painting methods, systematically applying the sequence of colors in the visible spectrum to real or imagined subjects, creating works that resonate across different environments and eras. Navigating between painting, installation, printmaking, and performance art, Ay-O embarked on an artistic adventure that transcended sensory limits with a mix of humor and critique. This quickly established his prominence in the international art scene.

In 1966, Ay-O represented Japan at the 33rd Venice Biennale with his Rainbow Tactile Room, a large-scale installation combining visual, tactile, and spatial elements. Visitors were not only overwhelmed by the sensory experience but also found their own ways to engage with the work. Driven by his obsession with color and influenced by both traditional Japanese Ukiyo-e and Pop Art, Ay-O embraced printmaking early in his career. He consistently pushed the boundaries of the medium, using bold, vibrant colors to create silkscreen prints that reflected his desire to explore the entire visible spectrum. His work Rainbow Hokusai, which won the Grand Prize at the 7th Tokyo International Print Biennale in 1970, remains a high bar for many artists today. In June 1987, Ay-O collaborated with the Paris municipal government to honor French painter Henri Rousseau (1844–1910) with the Ay-O Eiffel Tower Rainbow Project, hanging a 300-meter-long rainbow-colored ribbon from the top of the Eiffel Tower. Though the project only lasted three days, it became a notable example of Happening Art.

True to his belief that "art must be accessible," Ay-O has always considered himself a messenger of the rainbow. Using the rainbow as his symbol, he has crafted a clear path to inner peace through sensory experiences that blend reality and illusion—an especially rare accomplishment in today’s information-saturated world. Standing in front of his works, we can genuinely sense that we, too, can touch the rainbow and continue to hold on to joyful hopes for life.