Garshāsp (گرشاسپ) is the name of a monster-slaying hero in Iranian mythology. The Avestan form of his name is Kərəsāspa and in Middle Persian his name is Kirsāsp.
In the Zoroastrian religious text of the Avesta, Kərəsāspa appears as the slayer of ferocious monsters, including the Gandarəβa and the Aži Sruvara. In later Zoroastrian texts Kirsāsp is revived at the end of the world to defeat the monster Dahāg.
Kərəsāspa is the son of Θrita and belongs to the Sāma family. Θrita is originally the name of a deity; cf. the Vedic Trita.
According to the Zoroastrian holy book, Avesta, Kərəsāspa once stopped on a hill to cook his midday meal. Unbeknownst to Kərəsāspa, the hill was actually the curved back of a sleeping dragon—the Aži Sruvara. As Kərəsāspa's fire began to crackle merrily, the heat from it caused the dragon to stir from its sleep and overturn the hero's kettle. The startled Kərəsāspa fled, but, on regaining his composure, returned to slay the dragon that had spoilt his lunch.
Later texts, the Persian Rivayat and Pahlavi Rivayat, add more details. According to them, the Az ī Srūwar was a dragon with horns, with huge eyes and ears, and teeth upon which the men it had eaten could be seen impaled. It was so long that Kərəsāspa ran along its back for half a day before he reached its head, struck it with his mace, and killed it.
Another monster that Kirsāsp fought was the Gandarəβa, Middle Persian Gandarw. (This name is cognate to the Indic gandharva, but the exact way in which the word acquired its respective meanings in Indic and Iranian cultures is uncertain.) The Gandarw lived in the sea. It was also enormous, big enough to swallow twelve provinces in a single gulp, and so tall that when it stood up the deep sea reached only to its knee and its head was as high as the sun. The Gandarw pulled Kirsāsp into the ocean, and they fought for nine days. At last, Kirsāsp flayed the Gandarw and bound it with its own skin. Kirsāsp, weary from the combat, had his companion Axrūrag guard the Gandarw while he slept, but it proved too much for him – the Gandarw dragged Axrūrag and Kirsāsp's family into the sea. When Kirsāsp awakened, he rushed to the sea, freed the captives, and killed the Gandarw.