Origins
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Although his exact origins are unknown, the most commonly accepted theory is that he was derived from the Hindu deity Mahakala. Kageyama Haruki suggested that he may have been developed from the conflation of him and a deity that came to be known as Taizan Fukun in Japan. His name was possibly derived from the sanskrit word "mātṛkā" (transliterated as "mata" or "matara" in Japanese), which could link him to the Seven Matrikas who are pestilence deities. |
He came to be associated with noh theatre, the okina mask and silkworm breeding through Hata no Kawakatsu, a mythical person who's said to be an incarnation of him. The name Matarajin itself contains the kanji for "polish", "many times", "silk", and "kami" respectively, referencing this fact. Other variations contain the kanji for "be upset" and "mile" (Madarajin) and "steep" and "advantage" (Matarijin), but the first kanji always remains unchanged. Matarakishin simply uses katakana, plus the word "kishin", which simply means wrathful deity.
Matarajin-sama's exact areas of influence are many and thus it's hard to pin down his exact nature, which isn't at all unlike he himself. Still, I attempted to to get a better grasp on what he is and I did so with the image above, which lists every deity related to him one way or another, Buddhist or otherwise. The chart is centered on Matarajin-sama specifically and for that reason the only attributes listed are ones that are related to him.
Many thanks to Antonia (tumblr user yamayuandadu and wikipedia user HaniwaEnthusiast) who among many things contributed a lot to the historical and mythological internet presence of Matarajin-sama (via informative posts and completing his wikipedia page). Special thanks also to Mark Schumacher, owner of onmarkproductions for detailed information on Japanese Buddhism.