A samurai of the Matsushiro domain in Shinano Province (modern Nagano). A child prodigy who studied Confucianism under Sato Issai in Edo. Before Perry's arrival (1853), he recognized Western technological and military superiority, advocating "Eastern ethics, Western science." He experimented with cannon casting, telegraph machines, and glass manufacturing. His students included Yoshida Shoin, Katsu Kaishu, Sakamoto Ryoma, and Kobayashi Torasaburo—the brightest minds of the bakumatsu era. After Shoin's attempted stowaway incident, Shozan was placed under house arrest. In 1864, summoned by Hitotsubashi Yoshinobu, he went to Kyoto to advocate for national unity and opening the country. The sonnō jōi faction branded him a traitor, and on July 11, 1864, he was assassinated in broad daylight on Kyoto's Sanjo-Kiyamachi street by Kawakami Gensai. He was 54.

A thinker of overwhelming intellect and foresight. While flexible enough to fuse Eastern and Western learning, he was also supremely self-confident and arrogant, easily making enemies. His habit of riding horseback through Kyoto's streets drew the hatred of anti-foreign extremists.

His philosophy of "Eastern ethics, Western science" became an intellectual foundation of the Meiji Restoration. Through Yoshida Shoin he influenced Choshu activists, through Katsu Kaishu the shogunate reformers, and through Sakamoto Ryoma the Satsuma-Choshu Alliance. Ironically, the students he raised were the very ones who led Japan into the modern era he envisioned.