In Hittite mythology, Illuyanka was a serpentine dragon slain by Tarhunt, the Hittite incarnation of the Hurrian god of sky and storm. It is known from Hittite cuneiform tablets found at Çorum-Boğazköy, the former Hittite capital Hattusa. The context is a ritual of the Hattian spring festival of Puruli.
The myth is found in Catalogue des Textes Hittites 321, which gives two consecutive versions. In the first, the god Teshub successfully kills Illuyanka. In the second, Teshub loses instead, and Illuyanka takes his eyes and heart as proof of victory. To retrieve them, Teshub has his son Sarruma marry Illuyanka's daughter and ask for the return of the eyes and heart as a wedding gift. Restored, Teshub again challenges Illuyanka and is triumphant. However, Sarruma realizes he was merely used, and as the dragon dies, he demands his father destroy him as well. Teshub complies, killing Illuyanka and Sarruma with a raging storm.
"An dragon god that appeared in ancient Hittite legend. A violent god, he rules the sea. In many cultures around the ancient Orient, the rough waters and the river floods were often likened to dragons. There are many legends about him, including a tie when he fought the main god, the god of storms, in which he showed power greater than his opponent."
—Shin Megami Tensei IV Profile
Illuyanka is faced in the Challenge Quest, Slay the God of Violent Winds. Having defeated and stolen the heart and eyes of the God of the Storm, he resides in the area of Akasaka on the world map in Infernal Tokyo.