Goro Nyudo Masamune (c.1264–1343 AD) is widely regarded as the finest sword smith that Japan has ever seen. His samurai swords and daggers (tachi and tanto) were made in the Soshu tradition and he is believed to have worked in Sagami Province during the last part of the Kamakura Period (1288–1328).

The Fudo Masamune is one of the few surviving blades that is known for sure to have been made and signed by the legendary sword smith and from the early 1600s, it was in the possession of the Owari branch of the Tokugawa clan. It is a tanto, a dagger-like weapon made primarily for stabbing but with a sharp edge allowing it to be useful for slashing also.

The Fudo Masamune is approximately 25 cm long with a carving of roots on the Omote (Front, outer edge) side. It also has chopstick-like grooves (known as Gomabashi) on the back, a Dragon at the ura part of blade and features an engraving of Fudo Myo-o, the Buddhist deity (which gives the blade its name).

Source: wikipedia.org
Image: shibuiswords.com