Fudai daimyo were the daimyo, whom the TOKUGAWA clan had promoted from among the TOKUGAWA vassals at the service from before the Battle of Sekigahara (Sekigahara no Kassen).
関ヶ原の戦い（関ヶ原の合戦）以前より、徳川氏に臣従して取り立てられた大名を指す。