His original name was Matsudaira Takechiyo. Born to a minor warlord in Okazaki, Japan in 1543. He began his military training with the Imagawa family. He became allies with the powerful forces of Oda Nobunaga and then Toyotomi Hideyoshi, expanding his land holdings via a successful attack on the Hojo family to the east. After hideyoshi's death resulted in a power struggle among daimyo, Iesayu triumphed in the Battle of Sekigahara in 1600 and became shogun to Japan's imperial court in 1603.
What did he do for Japan?
Tokugawa founded the shogunate in Edo in 1603 ( Now known as Tokyo), that endured for more than 260 years after skillfully surviving a turbulent era of civil warfare .