*illu- "snake" in Hittite (cognate with English eel)
*anka- "snake" in Hurrian
The dragon slain by Taru/Teshub the storm god.
In one version of the story, Taru/Teshub battles Illuyankas at Kiškilušša, and is defeated by the dragon. Taru/Teshub asks the goddess Inaras for help, and she commands the hero Ḫupašiya to help her in return for sex. She lures the dragon to a cave, where he is given a feast and made drunk. Ḫupašiya binds the dragon, and Teshub and his children then enter the cave and kill him.
In a later version, Taru/Teshub and Illuyankas battle, and again Teshub loses--only this time, the dragon takes his eyes and heart. Years later, Taru/Teshub's son Sarruma goes to marry Illuyankas daughter. Taru/Teshub convinces his Sarruma to ask for his eyes and heart as a wedding present; once returned to Taru/Teshub, he goes to slay the dragon. However, his son sides with his new father-in-law, and is slain in the process.
The slaying of Illuyankas was apparently reenacted as part of a yearly spring ritual.
The storm god slaying the dragon is a familiar motif in Indo-European mythology; the story of Zeus and Typhon; Herakles and Ladon; Lludd and the dragons; Thor and Jǫrmungandr; Indra and Vrtra; arguably the extra-biblical interpretations of God and the Serpent*. The battle likely represents or has its origin in (among other things) the storm god's battle for supremacy over the waters, which the dragon hoards. In later times, the special treasure was transfered away from water specifically and onto other objects, such as the apples of the Hesperidies. However, this Hittite text, being extremely old, does like the Vedas refer directly to water.
*This brings up the difficulty of the relationshp between IE and Semitic mythologies, and what the nature of that relationship is, which is outside the scope of this node.
Beckman, Gary, "The Anatolian Myth of Illuyanka", JANES 14 (1982). URL: http://www.hittites.info/translations.aspx?text=translations/mythology%2fIlluyanka.html
Puhvel, Jaan. Comparative Mythology. Baltimore: Johns Hopkins University Press, 1989.