Toushirou blades are all made by a famous swordsmith, Toushirou Yoshimitsu from Awataguchi school. The name “Atsu” refers to the unusual thickness of the blade. He was handed down through shoguns of the Ashikaga clan and in the possession of among others Toyotomi Hidetsugu, Toyotomi Hideyoshi and Mōri Terumoto; presented to Tokugawa Ieyasu by the Mōri family. (heck, his lines about being used by a lot of famous person)
He is currently being kept in Tokyo National Museum as one of the National Treasures of Japan.
His name was originally read as Atsu Toushirou until 2015/08/25