Tadachika was the son of Okubo Tadayo. He fought at Anegawa, Mikatagahara, and the Komaki Campaign, serving as the commander of Tokugawa Ieyasu's bodyguard in the last. He inherited Odawara from his late father in 1593, and by 1603 was an important councilor for the Tokugawa house. He later fell out of favor, incurring the suspicion of Ieyasu and shôgun Tokugawa Hidetada, a situation worsened by a feud between Tadachika and Honda Masanobu. Tadachika was at length censored by the Tokugawa and while he was dispatched on an anti-Christian mission lost his lands in February 1614. His grandson Tadatomo was given back Odawara in 1687.
- Initial text from Samurai-Archives.com FWSeal & CEWest, 2005