In the introduction to The Book of Five Rings, Musashi identifies
himself as Shinmen Musashi no Kami Fujiwara no Genshin. Piecing
out the different parts of his name and why he does not call himself
Miyamoto, by which he is most widely known, takes a little explanation.
As a child Musashi went by the name Ben No Suke. Upon becoming
an adult (usually around age 13 at that time) he took the name Takezo,
which he began to pronounce as Musashi later. The two names are
different pronunciations of the same two Japanese kanji (symbols).
The first kanji has the meaning of warrior and is the same one used
in the words bushi and bushido, meaning warrior and
Way of the warrior. The second kanji in Musashi's name relates to
a type of storehouse.
Miyamoto is the town that Musashi came from and by which he was
most well know. In stressing his samurai lineage, he would use the
name Shinmen, which was the name of the Lord to which Musashi's
family was attached. The name Fujiwara also adds an touch of historical
pedigree by relating back to one of the four main Fujiwara famlies,
who were noble houses dating back to the eighth century. Finaly,
the name Genshin is a Buddhist name that Musashi chose.