Masamune was also known as Gorō Nyūdō Masamune, or Priest Gorō Masamune. He is thought to be Japan's greatest swordsmith. There are no exact dates known for Masamune's life and hence he has become almost a legend. It is believed that he made most of his swords in the late 13th and early 14th centuries between 1288 - 1328. He created swords, or tachi in Japanese, and daggers called tantō, in the Soshu tradition. It is believed that he lived and worked in the Sagami Province. Some old storeys list his family name as Okazaki, but some experts believe this was simply a storey to elevate the standing of the Tokugawa family.

At the Japanese Sword Making Competition an award exists for swordsmiths called the Masamune prize and it is not awarded every year, but it is only presented to a swordsmith who has created an exceptional work.

During the last part of the Kamakura Period, form 1288 - 1328, Masamune is believed to have worked in Sagami Province. It is thought that he was trained by swordsmiths from Bizen and Yamashiro provinces, such as Saburo Kunimune, Awataguchi Kunitsuna and Shintōgo Kunimitsu.