was daimyō of Odawara Domain in Sagami Province in early Edo period, Japan. Ōkubo Tadachika was the son of Ōkubo Tadayo, a hereditary vassal to the Tokugawa clan in what is now part of the city of Okazaki, Aichi. He entered into service as a samurai frm age 11, and took his first head in battle at the age of 16. He served in most of the campaigns of his father, including the Battle of Anegawa (1570), Battle of Mikatagahara (1573), Battle of Nagashino (1575), Battle of Komaki and Nagakute (1584), and Battle of Odawara (1590). He came to be regarded as one of Ieyasu's most experienced and trusted advisors, along with Honda Masanobu. In 1593, he was assigned the post of Karō to Tokugawa Hidetada. Upon the death of his father in 1594, he became head of the Ōkubo clan, and daimyō of Odawara Dom