A rangakusha was a Japanese intellectual, who studied foreign science. As this was prohibited by the Togkugawa regime, rangakushas pursued their forbidden knowledge in secret.
They procured foreign books on medicine, astronomy, math, physics, botany, geography, and military science through illicit channels. The most famous Rangakusha was Ito Genboku, who was held in custody at Edo Jail for his crimes of studying foreign medicine and carrying out experiments.