Koji Wakamatsu (若松孝二, Wakamatsu Koji?) (born 1 April 1936, in Wakuya, Miyagi, Japan) is a Japanese film director who directed such pinku eiga films as Ecstasy of the Angels (天使の恍惚 – Tenshi no Kokutsu) (1972) and Go, Go Second Time Virgin (ゆけゆけ二度目の処女 – Yuke, Yuke Nidome No Shojo) (1969). He also produced Nagisa Oshima’s controversial film In the Realm of the Senses (1976). He has been called « the most important director to emerge in the pink film genre, » and one of « Japan’s leading directors of the 1960s. » 
Wakamatsu worked as a construction worker before beginning his film career with Nikkatsu in 1963.  Between 1963 and 1965, he directed 20 exploitation films for the studio, based on sensational topics of the day. He became interested in the Pink Film genre after the success of Tetsuji Takechi’s 1964 Daydream. Nikkatsu submitted his Skeleton in the Closet (壁の中の秘事 – Kabe no naka no hibegoto) (also known as Secret Acts within Four Walls) (1965) to the Berlin International Film Festival while the film was still under review by Eirin, the Japanese film-rating board. This submission before passing Eirin’s review was doubly embarrassing for the government since pink films, though already emerging as the dominant domestic cinematic genre, were not regarded as worthy of critical attention or international export. The film received an enthusiastic reception at the festival, but Nikkatsu, fearful of governmental retaliatory action, gave it a low-profile domestic release. Disappointed, Wakamatsu quit the studio to form his own company.
Wakamatsu’s independent films of the late 1960s were very low-budget, but often artistically done works, usually concerned with sex and extreme violence mixed with political messages. Some critics have suggested that these films were an intentional provocation to the government, in order to generate free publicity resulting from censorship controversies.  His films were usually produced for less than 1,000,000 yen (about $5,000), necessitating extreme cost-cutting measures including location shooting, single-takes, and natural lighting. His early films were usually in black and white with occasional bursts of color for theatrical effect.
His first self-produced film was The Embryo Hunts In Secret (胎児が密猟する時 – Taiji ga Mitsuryo Suru Toki) (1966), a story of a man who kidnaps, tortures and sexually abuses a woman until she finally escapes and stabs him to death. Freeze-frames, flash-backs, hand-held camera and locations limited to two rooms and a hallway add to the film’s disturbing, claustrophobic atmosphere. Vagabond of Sex (Sei no Horo 1967) was a parody of Imamura’s A Man Vanishes (1967). In Wakamatsu’s film, a man leaves his family in Tokyo to travel and engage in various sexual escapades. When he returns home he finds out that his wife is starring in Imamura’s documentary about her search for her missing husband.
Violated Angels (犯された白衣 – Okasareta Hakui) (1967) was based on the murder of eight nursing students in the U.S. by Richard Speck. Dark Story of a Japanese Rapist (日本暴行暗黒史 – Nihon Boko Ankokushi) (1969) was based on a serial-rapist case in Japan after World War II. One of his most critically esteemed films is Sacred Mother Kannon (聖母観音大菩薩 – Seibo Kannon Daibosatsu) (1977), which has been called a « ‘text book example’ for the use of metaphor and symbolism in contemporary cinema. » 
While directing many successful and critically praised Pink Films, Wakamatsu also became known for giving young filmmakers their first experience in working in the industry. Among those whose early careers were helped by Wakamatsu are Banmei Takahashi, Genji Nakamura and Hiroshi Mukai.