Wikipedia
Azhdaha, Azhdahak, Ezhdeha or Azhdar is a mythical creature in Iranian mythology, roundly equal to Dragon. They are gigantic snake-like creatures living in the air, in the sea, or on earth. Sad dar-e nathr and sad dar-e Bondahesh, Shahnameh and Garshaspnameh are among main principal texts that contain information about the creature. In Persian literature, Azhdahas are depicted as a giant snake or lizard with wings.
According to traditions, they have a huge body, a very scary face, their mouths are wide with lots of teeth, and their eyes are bright. Azhdahās are actually normal snakes, according to "Ajāyeb ul-Makhlooghāt", a book by Mohammad b. Mahmoud b. Ahmad-e Tusi (wrote in 1160 AD), "when a snake lives 100 years and its length becomes 30 Gazes, it is called an azhdahā". He also wrote that "because of their harassment to other creatures, the God eventually will throw them in the sea and in there, their body continue to raise, such that their length becomes more than 10,000 Gazes (a traditional measurement unit roundly equal to a meter). Then in the sea, they evolve to have two wings, like a fish, and the seawave is because of their movements. Eating the heart of an Azhdahā brings courage and bravery. Their skins are suitable to healing the wound of love, and if someone bury an azhdahā's head in a land, the conditions of that land will become good."
In Shahnameh, the national epic of Greater Iran, Azhdahas appear in a number of stories. Sām, Rostam, Esfandiar, Eskandar, Bahram V (Gur) are among the heroes that kill a dragon.