Ferdousi and criticism of Sassanid and Ghaznavid politics through Ghoshtasb's change of character in Shahnameh

One of the characters whose presence in Shahnameh creates bitter and painful events is Ghoshtasb. The image of this Kiani king in Shahnameh is different from the images drawn in religious texts be it Avesta or Pahlavi. While in Shahnameh he is a shortsighted, voracious, vow breaker and selfish, in Avesta and Pahlavi texts, he is quite holy.
May be in the mind of the reader of Shahnameh this question arises: How such a reversal in character has appeared had Ferdousi been fidel to the sources he had used according to his own emphasis in Shahnameh?
It is the purpose of this article to explain the factors responsible for this change of character. It could be assumed that one factor is ferdousi’s and other patriots’ opposition towards the Turk or Arab rulers. Ghoshtasb’s change of character is the product of political aims of the poet and the narrators who have published narratives contrary to the Zoroastrian religious texts. Since with Ghoshtasb’s change of character, Sassanid who claimed to be related to Ghoshtasb were criticized that is a governorship which Mahmud Ghaznavi claimed to be related to and of course to a great extent his reign resembled that of Sassanid. Therefore in this way the poet reveals the true picture of Turks and Arabs kingdom which followed the same example of Sassanid and turned toward religious dictatorship and centralization of power. Ferdousi and his fellow thinkers changed the character of Ghoshtasb to fight with all those who thought, spoke and acted like him.