Titles: Echizen no Kami, Mutsu no Kami
Also known as: birth—Bontenmaru (梵天丸), adult—Tojirou (藤次郎), posthumous—Teizan (貞山), self-introduction—Fujiwara no Masamune (藤原政宗), religious—Takeru Hikonomikoto (武振彦命), nickname—One-Eyed Dragon (独眼竜)
Date Masamune was a powerful daimyo in the Northeastern part of Japan during the Sengoku Period. He was the 17th-generation head of the Date Clan and the founding daimyo of Sendai-han. He was the eldest son of Date Terumune and Yoshihime, the daughter of Mogami Yoshimori.
Masamune was born in Yonezawa Castle (modern-day Yamagata Prefecture). He lost the use of his right eye after falling ill of smallpox in his childhood, and would later come to be known as the One-eyed Dragon. However, because of it his mother thought him unfit for rule of the clan, and favored his younger brother. When Date Terumune retired from the position of the clan head in 1584, Masamune killed his brother and became the head of the clan at 18.
Masamune was known as a brilliant tactician. Shortly after he became head of the clan, Oouchi Sadatsuna, a Date vassal, defected to the Ashina Clan in the Aizu region of Mutsu Province. Masamune declared war on the Ashina for the betrayal, but was forced to retreat by the Ashina general, Iwashiro Morikuni. Three months later, Masamune laid seige to Oouchi's stronghold at Otemori. It was said that he put some 800 people to the sword in retaliation for the betrayal. Thereafter the Hatakeyama Clan, the traditional rival of the Date Clan, kidnapped Masamune's father, who was then killed in battle when Masamune and his troops engaged the kidnappers. War ensued between the two clans, and Masamune would ruthlessly subjugate his neighboring clans, even those who were allied by marriage or kinship. He defeated the Ashina Clan in 1589, but was called by Toyotomi Hideyoshi to lay siege to Odawara Castle of the Houjou Clan.
He served both Toyotomi Hideyoshi and Tokugawa Ieyasu, though neither trusted him completely due to his ambition and aggression. Under Tokugawa Ieyasu Masamune controlled one of the largest fiefdoms in Japan and turned Sendai from a small fishing village to a large and prosperous city. He encouraged foreigners and was largely lenient towards Christanity and its practioners. He funded and backed the first Japanese expedition to sail around the world, which visited such places as the Philippines, Mexico, Spain and Pope Paul V in Rome.
He died in Edo at the age of 70 of esophageal cancer, and was entombed in the Zuihouden according to his last will and testament. His second son (eldest son by his legal wife Megohime) Date Tadamune inherited the position of clan head after him.