Jamshid, in the Iranian mythological and epic tradition, possesses a dual and contradictory nature. On one hand, he is the most charismatic king and the founder of the "Golden Age," a utopia free from death, old age, and disease. On the other hand, he is the first great sinner whose transgression leads to the collapse of this utopia and the return of evil to the world. The fundamental problem addressed in this research is the explanation of the "confusion" and "plurality" of narratives regarding the nature of Jamshid's sin in Iranian texts. Ancient sources offer no single explanation for his fall; reasons vary from "pride and claiming divinity" to "lying," "foolishness," "meat-eating," and even "refusing divine prophethood." Conversely, texts like Kushnameh portray him as a pious monotheist until the end of his life. This study posits that this narrative confusion is not a weakness but a sign of a profound discursive shift. It aims to uncover the roots of these contradictions by employing a comparative-analytical method and examining older layers in Indian mythology (Vedic and Puranic), demonstrating how the concept of sin was re-arranged in the transition from the Indo-Iranian to the Zoroastrian tradition.