- Born: 1658
- Died: 1714/11/2
- Titles: soba yônin (1688-?), Rôjû & Tairô (1706/1/11-1709/6/3), Dewa-no-kami, Mino-no-kami
- Other Names: 柳沢保明 (Yanagisawa Yasuakira), 松平吉保 (Matsudaira Yoshiyasu), Fusayasu, Yatarô, Hozan, Shôshô Yoshiyasu
- Japanese: 柳沢吉保 (Yanagisawa Yoshiyasu)
Previously known as Fusayasu and Yasuakira, he was born into a samurai family, and was initially a mere page (koshô) within the shogunate, with a stipend of 150 koku. However, at some point, he became a personal favorite of Shogun Tokugawa Tsunayoshi, and was promoted to a fief of 32,030 koku, and was granted the privilege of the use of the clan name Matsudaira. He became soba yônin under Shogun Tokugawa Tsunayoshi in 1688, and was visited directly at his home by the Shogun on nearly sixty occasions, beginning with a visit on 1691/3/22.
Yoshiyasu became lord of the 150,000 koku domain of Kôfu in 1704, and then rôjû and Tairô in 1706, serving in that position until 1709. At the peak of his status, he claimed a fief of some 228,765 koku.
He is known as an avid patron of Chinese thought and culture, inviting a number of Chinese Ôbaku Zen monks, as well as Nagasaki-based Japanese scholars of colloquial Chinese language and culture, to his mansions, and appointing Ogyû Sorai as a scholar in his service. Yanagisawa also sponsored discussions, sometimes attended by the shogun, of Confucian classics, conducted in Chinese; in connection with this, he also organized language classes in colloquial Chinese which served as the basis for Sorai's own study of the language. When the Chinese monk Eppô was interviewed by Tsunayoshi in 1705, it is said that Yanagisawa was the only one in the room who did not need to wait for the interpreters to understand what was being said.
- Arai Hakuseki, Joyce Ackroyd (trans.), Told Round a Brushwood Fire, University of Tokyo Press (1979), 311n31.
- Plaques on-site at Rikugien.
- Cecilia Segawa Seigle, “Tokugawa Tsunayoshi and the Formation of Edo Castle Rituals of Giving,” in Martha Chaiklin (ed.), Mediated by Gifts: Politics and Society in Japan 1350-1850, Brill (2017), 131-133.
- Marius Jansen, China in the Tokugawa World, Harvard University Press (1992), 56-57.