Who they were
Date Masamune was the “One-Eyed Dragon” of the north: he lost his right eye to childhood smallpox, and his crescent-moon helmet is iconic. In his youth he unified much of the Tohoku region.
What they did
He submitted to Toyotomi Hideyoshi in 1590 and sided with Tokugawa Ieyasu at Sekigahara, and was confirmed in a great northern domain. There he began building Sendai Castle in 1600 and developed the castle town and agriculture around it. He dispatched the Keicho embassy (1613–1620): his retainer Hasekura Tsunenaga crossed the Pacific and the Atlantic, reaching Spain and Rome — the first Japanese diplomatic mission across both oceans — though the hoped-for trade came to nothing as Japan closed to Christianity. He died in 1636.
Legacy
Masamune is honored as the founder-hero of Sendai and remains the flamboyant favorite of Sengoku popular culture.