Career
Tadatoshi was the son of Aoyama Tadanari, a Tokugawa vassal of the Sengoku period who was born in Mikawa Province. Tadatoshi, like his father, was a Tokugawa vassal, and was famous for his role as the third shogun Iemitsu"s teacher. He became a daimyo in 1603, when Tokugawa Ieyasu granted him the domain of Edosaki.