Amatsumara is a deity of ironworking that appears in Japanese mythology. He appears in the "Kojiki" (The Records of Ancient Matters) but not in "Nihonshoki" (Chronicles of Japan). He has none of the titles, such as "kami" or "mikoto," that are usually given to Shinto deities.
Amatsumara appears in the Iwatogakure section of the "Kojiki," which relates how the sun goddess, Amaterasu, hid in a cave and was lured out uing a mirror and the dancing of Amenouzume, the goddess of merriment. The "Kojiki" states that the 'blacksmith, Amatsumara was called upon' but there is no description of what he did. The sentence before that states that Amatsumara was 'using steel from the metal mountain of heaven,' so he is believed to have been refining the iron used by Ishikoridome to make the mirror. The main text of the "Nihonshoki" says that Amenouzume was holding an enchanted spear, Chimaki no Hoko, but there is no description of its maker. This can be interpreted to mean that Amatsumara made the spear (The first addendum indicates that Ishikoridome made the hiboko (spear)).
The section on tensonkorin (the descent to earth of the grandson of the sun goddess) in "Sendai Kujihongi" (Ancient Japanese History) reads 'the ancestor of Yamato no Kanachi and others called Amatsumaura' and 'the ancestor of Mononobe no Miyatsuko and others called Amatsumara and the ancestor of Ato no Miyatsuko and others called Amenomara,' all of which are considered to be the same deity as Amatsumara. Another theory states that since there is no divine title, Amatsumara is not the name of a god but a general term for blacksmiths (or their deified ancestor).
"Amatsu" in the name "Amatsumara" refers to the Amatsukami (gods of heaven), but there are several theories as to the meaning of 'mara.'
One theory states that 'mara' comes from 'me-ura' meaning 'one-eyed,' a reference to the practice of blacksmiths closing one eye in order to check the iron's temperature from its color (or to an occupational hazard of blacksmiths).
Another theory states that 'mara' is a Mongolian word that means iron.
There is also a theory that blacksmith's hammers were compared to a penis and so 'mara,' a slang word for penis, became part of the name.
(It should be noted, however, that since the word "mara," which means 'obstacles to practicing buddhism,' was introduced to Japan together with Buddhism and only later came to be used as another word for penis, this theory is an invention by more recent generations.)
If the first theory is accepted, Amatsumara can be held to be the same deity as Amenomahitotsu no kami (the one-eyed kami of heaven), who appears in "Nihonshoki" and "Kogo-shui" (History of the Inbe clan). Amenomahitotsu no kami was also a deity of ironworking, and in "Kogo-shui," he made metal weapons at the time of Amaterasu's hiding away in the cave.