Yokoo Tadanori and Keiichi Tanaami are the best-known exponents of the Japanese Ungurashibai poster style, closely tied to radical underground theatre and animation. In the late 60s and early 70s their work combined traditional Japanese imagery with psychedelia and radical politics. It's sometimes referred to as Neo-Roman Baroque.
Both men continue their work today. They're colourful personalities. Tadanori, a celebrity in Japan, was closely connected with the brilliant underground theatre and film director Shuji Terayama. He has made many trips to India (some with YMO's Haruomi Hosono), met Salvador Dali, worked with The Beatles and is known as an expert in UFOs. He also starred in Oshima's film Diary of a Shinjuku Thief.
Tanaami, known for his Gilliamesque animations, teaches art and works in photos and multimedia today. The book Blow Up has recently collected his work between 1963 and 1974. In the introduction he says 'Most of my works in the 60s, including posters and graphic design, were silkscreen prints. Unlike modern ink that has no life, the ink used in the 60s emitted a unique smell and character throughout the room as soon as a newly-printed poster was hung on the wall... The power that 60s silkscreens exude seems to me to symbolize the era's energy.'
Here's a feature about Yokoo Tadanori from Metropolis magazine.