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 𐬔𐬀𐬌𐬌𐬊 𐬨𐬆𐬭𐬆𐬙𐬀𐬥 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 𐭪𐭣𐭬𐭫𐭲 Kayōmart. In Ferdowsi's Shahnameh he appears as the first shah of the world. He is also called the pišdād (پيشداد), the first to practice justice, the lawgiver.

The Avestan form means "the living mortal", from gaya 'life' and marətan 'mortal, human being'; cf. Persian mard 'human' (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 marətan 'mortal'.

In the eighth book of the Denkard, a reference is made to the lost Chihrdad section (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:

Gayōmart Gar-shāh (King of the Mountains) was the first human Uhrmazd created. Before Gayōmart came, in the fifth "Gāh" (Ahura Mazda created the world in six Gāhs) Gavevagdāt (the primordial ox) had been created from mud in Erān-vēdj (which was the middle of the earth) on the right side of the river "Veh-Dāit" ... In the sixth "Gāh" Gayōmart was created from mud ... on the left side of "Veh-Dāit", to help Uhrmazd and he was created in the form of a 15-year-old boy. They lived for 3000 years in peace, neither eating, speaking nor praying, although Gayōmart was inwardly considering these things. At the end of this 3000-year period (during which Ahriman lay stunned by Uhrmazd's Ahunawar incantation and could do nothing) Jēh (the demonic whore) cried out, awakening him ... whereupon Ahriman and his minions the Dīvs fought with the light and, on the first day of spring (i.e. the 1st of Farvardin, the Iranian New Year) Ahriman leaped forth onto the earth in the form of a dragon. He started to create death, illness, lust, thirst, hunger among all living things and disseminated throughout the world the Kyrm (the class of evil creeping things which includes reptiles, insects and rodents) [...] In the catastrophe Gavevagdāt died (this being also the symbol of the old year giving way to the new, as depicted in Persepolis reliefs); and Ahriman left "Astovidat" (a Dīv) to guard Gayōmart, but could not kill him because his time had not yet come [...] he lived for 30 years afterwards and, when, finally, he died, fell upon his left side and shed his semen upon the ground, which was then fertilized by the sun [...] and after 40 years there grew Mashya and Mashyana as two rhubarb plants ..."^{[1][page needed]}

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 xvarənah), reserved for kings. His son Siāmak (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 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 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.

• Cosmic Man

• Abolqasem Ferdowsi (2006). Shahnameh: The Persian Book of Kings. Translated by Davis, Dick. Viking Adult. ISBN 978-0-670-03485-7. Modern English translation (abridged).
• Aghaee, Shirzad (1993). Nām-e kasān va jāyhā dar Shāhnāme-ye Ferdowsī نام كسان و جايها در شاهنامه فردوسى [Personalities and places in the Shahnameh of Ferdowsi]. Nyköping, Sweden: Behrang. ISBN 91-630-1959-0.
• Cereti, Carlo (2015). "Gayōmard (Article 2)". In Yarshater, Ehsan (ed.). Encyclopædia Iranica, Online Edition. Encyclopædia Iranica Foundation. Retrieved 13 April 2024.
• Safa, Zabihollah (2000) [1945]. Ḥamāse-sarāyī dar Īrān حماسه‌سرایی در ایران [Epic poetry in Iran] (in Persian). Tehran.{{cite book}}: CS1 maint: location missing publisher (link)
• Shaki, Mansour (2000). "Gayōmart". In Yarshater, Ehsan (ed.). Encyclopædia Iranica, Online Edition. Encyclopædia Iranica Foundation. Retrieved 13 April 2024.
• The Shahnama of Firdausi. Translated by Warner, Arthur; Warner, Edmond. 9 vols. London: Keegan Paul. 1905–1925.{{cite book}}: CS1 maint: others (link) (complete English verse translation)

• A King's Book of Kings: the Shah-nameh of Shah Tahmasp, an exhibition catalog from the Metropolitan Museum of Art (fully available online as PDF), which contains material on Keyumars