Keyumars or Kiomars (Persian: کیومرث) was the name of the first king (shah) of the Pishdadian dynasty of Iran according to the Shahnameh.
The name appears in Avestan in the form of Avestan: {{script|Avst| Avestan: Gaiio Mərətan, or in medieval Zoroastrian texts as Gayōmard or Gayōmart. In the Avesta he is the mythological first human being in the world. The corresponding name in Middle Persian is Pahlavi: Pahlavi: Kayōmart. In Ferdowsi's Shahnameh he appears as the first shah of the world. He is also called the Persian: pišdād (Persian: پيشداد), the first to practice justice, the lawgiver.
The Avestan form means "the living mortal", from Avestan: gaya 'life' and Avestan: marətan 'mortal, human being'; cf. Persian Persian: mard 'human' (Persian: مَرد).
Keyumars is also a popular first name in Persian speaking countries (Iran, Afghanistan and Tajikistan).
According to the Zoroastrian creation myth, Gayōmart, who was neither male nor female, was the first human, or, according to the Avesta, he was the first person to worship Ahura Mazda. The Avestan forms Mashya and Mashyana appear as the male and female first humans; their names are versions of the word Avestan: marətan 'mortal'.
In the eighth book of the Denkard, a reference is made to the lost Chihrdad section (Pahlavi: nask of the Avesta, which is divided into 21 sections. Apparently, this section dealt with how the world and mankind were created, including the creation of Gayōmart. References are also made to the Varshtmānsar section, which also included information about Gayōmart which Ahura Mazda had given to Zoroaster: "For 30 centuries I kept the world from corruption and decay, when the 30th century came to an end the Dīvs assaulted Gayōmart ... But I finally repelled them and plunged them into the darkness".
A concise summary of the story of Gayōmart according to Middle Persian texts is given by Zabihollah Safa:In the Avesta, Gayōmart is named as the pure and righteous, and according to Zoroastrian tradition the genealogy of Zoroaster can be traced through 45 generations to him.
Ferdowsi's 11th-century epic poem, the Shahnameh, begins with the story of Keyumars. He was the first king to arise among humans, who at that time lived in mountain caves and wore the skins of leopards. Keyumars was also the first human to introduce royal practices and the preparation of food and was also the first practitioner of law and justice. He was so powerful that all humans, tame animals, and wild animals paid homage to him. God (Ahura Mazda) granted Keyumars the supernatural radiance called the farr (Avestan Avestan: [[Khvarenah|xvarənah]]), reserved for kings. His son Siāmak (Persian: سیامک) was beloved of all except the Devil, Ahriman, who raised an army under the command of his own demonic son. When the angel Sorush (Avestan Avestan: [[Sraosha|Sraoša]]) warned Keyumars, Siāmak led an army of his own. Siāmak accepted a challenge to single combat and died at the hands of the demon.
Keyumars mourned for a year, and then Sorush advised him to fight Ahriman once more. Siāmak's son Hushang (Avestan Avestan: Haošyaŋha) was grown by this time and led the army that defeated Ahriman's son, who was bound and beheaded. Keyumars died after a thirty-year reign, leaving his throne to Hushang.