Based on an actual sword smith from the feudal period in Japan, he was also known as Gorō Nyūdō Masamune, he was said to have lived c.1264–1343.
No exact dates are known for Masamune's life, though it is generally thought that he created his vaunted swords in the late 13th and early 14th centuries.
A fictional version of Masamune is referenced by Juan Sanchez Villa Lobos Ramirez in the 1986 film. According to Ramirez, Masamune, a nobleman and a genius, created his ivory-handled katana for him in 593 BC. It was made in secret, using metallurgical techniques that would not become common until centuries later. This katana was a wedding gift for Ramirez in his marriage to Masamune's daughter, Shakiko.
In the comics, Masamune's adopted Immortal son, the ruthless and power-hungry Ren, would covet the sword, which would lead to a fatal conflict with Ramirez's student, Connor MacLeod, in 1966.
Highlander: The Series
The actual sword smith, Gorō Nyūdō Masamune, is alluded to in Season 1's "Free Fall." Duncan MacLeod and Tessa Noël acquired a katana made by Masamune from a private seller. Upon meeting Felicia Martins, Duncan trained her in sword fighting and gave her the Masamune katana. Duncan told Felicia "Take care of it, make it a part of you."
Unfortunately, the Masamune katana was broken by Duncan after Felicia betrayed him and attempted to take his head. Despite the katana having been made by the great swordsmith, Duncan's dragonhead katana proved to be the superior blade.
In the script for the 1986 film, Masamune was originally named Kamakura.