Thagirion is the sixth Qlipha, the shadow of Tiphareth, the sphere of Beauty. Read as "the disputers" or those who make ugliness where beauty should be, it is imaged as a blackened sun, also spelled Tagaririm.
In the scheme followed here it is ruled by Belphegor, whose name derives from Ba'al Pe'or, the Moabite god at whose shrine the Israelites were said to have joined themselves at Numbers 25, an episode read there as a grave apostasy. Later Christian demonology, including one influential seventeenth century classification of demons by the sin each tempts toward, cast Belphegor specifically as a demon of sloth or of false discovery, a considerably narrower role than the biblical fertility god the name began as. The pairing with Tiphareth, whose beauty and harmony are said to curdle into a blackened, dissonant sun in this shell, is a later Kabbalistic reading with no equivalent in the older material about Ba'al Pe'or itself. Spellings and rulers of the shells vary by source; the material is presented academically.
Tiphareth is attributed to the Sun, and the blackened sun imagined for Thagirion is read as that same solar harmony eclipsed, beauty's ordering center gone dark rather than radiant, a corruption fitted precisely to the sephirah it shadows.