Lifespan: 2/10 of Tenshō 6 (1578) to 4/15 of Kanei 20 (1643)
Rank: bushō, daimyō
Title: Junior Fifth Rank (Lower), Governor of Hōki
Clan: Aoyama branch of the Kasanoin lineage of the Fujiwara-Hokke
Domain: Hitachi-Edosaki, Musashi-Iwatsuki, Kazusa-Ōtaki
Lord: Tokugawa Ieyasu → Tokugawa Hidetada
Father: Aoyama Tadanari
Mother: Daughter of Amakata Michioki
Siblings: Tadatsugu, Tadatoshi, Asahina Yasushige, Yukinari, Amakata Michinao, sister (wife of Kawaguchi Chikatsugu)
Wife: Daughter of Ōkubo Tadasuke
Children: Munetoshi, Munesuke, Munehide, Masatoshi, daughter (formal wife of Takigawa Masatoshi), Jushōin, daughter (wife of Kawaguchi Masanobu), daughter (wife of Nakane Masatsugu)
Aoyama Tadatoshi served as a bushō during the Azuchi-Momoyama period and hereditary daimyō of the Edo bakufu during early Edo period.
The Aoyama clan originated in the Aoyama township in the Agatsuma District of Kōzuke Province and, later, settled in the village of Dōdō in the Nukata District of Mikawa Province. From this location, the Aoyama began to serve the Matsudaira clan.
Tadatoshi served as the second lord of the Hitachi-Edosaki domain, the lord of the Musashi-Iwatsuki domain, and the lord of the Kazusa-Ōtaki domain. He was the tenth head of the main branch of the Aoyama family and received the court titles of Junior Fifth Rank (Lower) and Governor of Hōki. He frequently admonished Tokugawa Iemitsu and, as a result, was removed from his position.
In 1578, Tadatoshi was born as the second son of Aoyama Tadanari in Hamamatsu in Tōtōmi Province.
His first experience in battle occurred at the Conquest of Odawara. Owing to the premature death of his older brother, Aoyama Tadatsugu, Tadatoshi became the lineal heir to the family. His father, Tadanari, served Tokugawa Ieyasu so, initially, he served Ieyasu. Later, he served Tokugawa Hidetada, the second shōgun of the Edo bakufu.
From 1600, Tadatoshi was named Hōki-no-kami, or Governor of Hōki. In 1603, he was awarded a fief of 5,000 koku. In 1607, Tadatoshi, together with Doi Toshikatsu and Sakai Tadayo, served as mentors for Tokugawa Iemitsu. In 1610, his fief was increased by 5,000 koku, yielding a total of 10,000 koku by which he attained the status of an independent daimyō. In 1613, upon the death of his father, Tadatoshi became the second lord of the Hitachi-Edosaki domain.
In 1615, Tadatoshi became a member of the council of elders for the bakufu. In 1620, he became the lord of Iwatsuki Castle with a fief of 55,000 koku in the Saitama District of Musashi Province.
Owing, however, to his frequent admonishments of Iemitsu, on 10/19 of Genna 9 (1623), he was removed from his role on the council of elders and transferred with a reduced fief of 20,000 koku to the Kazusa-Ōtaki domain. Thereafter, in 1625, he lost his fief and, after passing-through Amido in Shimōsa Province, 溝郷 in Sagami Province, and Kobayashi in Tōtōmi Province, he was confined to Imaizumi in Sagami. After the death of Hidetada in 1651, he was requested to serve again but refused. His eldest son, Aoyama Munetoshi, served as a hatamoto and daimyō and his second son, Aoyama Munesuke, served as hatamoto for the Edo bakufu.
In 1643, Tadatoshi died at the age of sixty-six.