What is "shabrang"

In Persian mythology, Shabrang, full name Shabrang Behzād literally "night-coloured purebred", was the horse of the hero Siyâvash. In a trial of his righteousness, Siyâvash passed through a large fire riding this stallion. After his death, his son Kai Khosrow, eventually became the ruler of Persia and was among the most magnificent and benevolent rulers according to Shahnameh. He disappeared and in traditional Zoroastrian mythology, he never died and will return to bring justice riding on his father's horse Shabrang.