Susumu Hirasawa (平沢進, Hirasawa Susumu; born April 2, 1954) is a Japanese musician and composer. He is well known for his work for the films of director Satoshi Kon and the animated adaptations of the Berserk manga series, alongside his work as a solo artist and as a member of P-Model.

Hirasawa was born on April 2, 1954, to his father Kiyoshi (平沢 清), a firefighter as well as a calligrapher. Under the penname "Hōseki" (峰石), he wrote the names of album and band for the cover art of the P-Model album Potpourri. Hirasawa lived with his older brother, artist Yūichi (平沢 裕一, born October 5, 1950), who goes by the moniker "YOU1". He formed a stage effects team for Mandrake and appeared at the band's final show, running on a treadmill. Yūichi was P-Model's art director for the band's first 9 years of existence, and has done occasional artwork for his brother from 2013 onwards. His only musical credits are for writing the lyrics of "For Kids" and "Sunshine City" (from In a Model Room), and for doing backing vocals on "Rocket" (from The Ghost in Science).

Since childhood, Hirasawa had an interest in machinery, and thought of himself as an engineer. He was an RC plane enthusiast, wanting to be a pilot, and repaired broken devices like radios and flashlights given to him by his parents. He studied in the electronics department of Honjo Technical High School [ja], where he was the first to finish the graduation project, the construction of a TV, despite the fact he did not fully understand the circuits. He also had motocross as a hobby.

He enrolled in the Tokyo Designer Gakuin College [ja] in 1972 and graduated cum laude in 1975 from the university's interior design course. According to the Tokyo Designers' Gakuin College '75 Design Annual, his graduation project was a dome-shaped stage set hall for Tangerine Dream's performances.

In his fifth year of elementary school, Hirasawa learned to play the electric guitar, inspired by the surf and instrumental rock bands he heard on the radio and on TV, later joining his junior high school's band. In 1973 he formed Mandrake, a progressive rock band that incorporated elements from heavy metal and krautrock together. Being one of the few Japanese progressive rock bands of its time, Mandrake achieved little success and released no albums during its lifetime.

During the early days of Mandrake, he worked as a part-time carrier on a fruits and vegetables market during the morning and at a Pepsi warehouse during the night, alongside Mandrake co-founder Fumiyasu Abe. In 1978, Hirasawa applied for a part-time lecturer position at Yamaha Music Foundation, and got the job, as he was the only person who applied. He taught courses at the Yamaha Synthesizer School until 1983, and met various musicians that he would later collaborate with through these lectures. After leaving his position as teacher, he took to making commercial jingles for the rest of the decade to make ends meet.

After discovering punk rock and working on synthesizer-heavy projects, Hirasawa decided to change the band into the electronic rock band P-Model in 1979. Initially met with success, they changed to the unpopular post-punk and experimental rock genres after Hirasawa went through an adverse reaction to his fame. With Hirasawa at the forefront, the band went through various lineups and achieved some popularity in the Japanese independent music scene.

In 1989, Hirasawa launched his solo career with the release of the album Water in Time and Space. His music incorporated elements from other genres, alongside themes from philosophy and psychology. He continued to change his musical style while concurrently working with two different iterations of P-Model until the group was disbanded in 2000. He has been actively releasing new music since then.