Atar, Atash, Azar (𐬁𐬙𐬀𐬭) or Dāštāɣni, is the Zoroastrian concept of holy fire, sometimes described in abstract terms as "burning and unburning fire" or "visible and invisible fire" (Mirza, 1987:389). It is considered to be the visible presence of Ahura Mazda and his Asha through the eponymous Yazata. The rituals for purifying a fire are performed 1,128 times a year.
In the Avestan language, ātar is an attribute of sources of heat and light, of which the nominative singular form is ātarš, source of Persian ātaš (fire). It was once thought to be etymologically related to the Avestan āθrauuan / aθaurun (Vedic atharvan), a type of priest, but that is now considered unlikely (Boyce, 2002:16). The ultimate etymology of ātar, previously unknown (Boyce, 2002:1), is now believed to be from the Indo-European *hxehxtr- 'fire'. This would make it related to Latin ater (black) and possibly a cognate of Albanian vatër, Romanian vatră and Serbo-Croatian vatra (fire).
In later Zoroastrianism, ātar (Middle Persian: 𐭠𐭲𐭥𐭥𐭩 ādar or ādur) is iconographically conflated with fire itself, which in Middle Persian is 𐭠𐭲𐭧𐭱 ātaxsh, one of the primary objects of Zoroastrian symbolism.
Atar is already evident in the Gathas, the oldest texts of the compendium of the Avesta and believed to have been composed by Zoroaster himself. At this juncture, as in the Yasna Haptanghaiti (the seven-chapter Yasna that structurally interrupts the Gathas and is linguistically as old as the Gathas themselves), atar is still—with only one exception—an abstract concept simply an instrument, a medium, of the Creator and is not yet the divinity (yazata) of heat and light that atar was to become in the later texts.
In the most ancient texts, atar is a medium, a faculty, through which judgement is passed and reflects the pre-Zoroastrian institution of ordeal by heat (Avestan: garmo-varah, heat ordeal; cf. Boyce 1996:ch. 6). Justice is administered through atar (Yasna 31.3, 34.4, 36.2, 47.2), the blazing atar (31.19, 51.9), through the heat of atar (43.