Sheikh Shams ad-Din, known in Kurmanji as Şêşims, is one of the seven Holy Beings of the Yezidi Heptad and one of its most fundamental theological symbols. His name means 'sun of the religion', and he is identified directly with the Sun as the source of light and life and as the divine light of God; he is correspondingly associated with fire, the sun's earthly counterpart, and his shrine at Lalish is the place at whose doorway Yezidis swear their most solemn oaths and before which a bull is sacrificed during the Feast of the Assembly. On the earthly plane he is reckoned the eldest of the four sons of the prince Êzdîna Mîr, who ruled the community before Sheikh Adi's arrival, and he is the eponymous ancestor of the Şemsanî branch of the sheikh caste. With his brother Fexredîn, who personifies the Moon, he forms a complementary solar–lunar pair among the group known as the Four Mysteries.