Tokugawa Tadanaga (徳川忠長: 1606–1633) was a Japanese daimyo of the early Edo period. The son of the second shogun Tokugawa Hidetada, his elder brother was the third shogun Tokugawa Iemitsu. Often called Suruga Dainagon (the major counsellor of Suruga), Tadanaga was born in 1606. The date of his birth is uncertain, and is variously given as May 7, June 1, and December 3. As a youth, he received support from his mother, Oeyo (or Sūgen'in), who favored him over her other son Iemitsu to become the third shogun. Later, his misconduct resulted in his being stripped of office, and he committed seppuku.