Mehregān Persian festival celebrated to honor the yazata Mithra (Persian: Mehr), which is responsible for friendship, affection and love. It is also widely referred to as the Persian Festival of Autumn.
According to The Wiley-Blackwell Companion to Zoroastrianism (2015), it was originally a feast honoring the Zoroastrian yazata Mithra. By the 4th century BCE, it was observed as one of the name-day feasts, a form it retains in today. Still, in a predominantly Muslim Iran, it is one of the two pre-Islamic festivals that continue to be celebrated by the public at large: Mehrgān, dedicated to Mithra (modern Mehr), and Tirgan, dedicated to Tishtrya (modern Tir).
Name-day feasts are festivals celebrated on the day of the year when the day-name and month-name dedicated to a particular angel or virtue intersect. The Mehr day in the Mehr month corresponded to the day farmers harvested their crops. They thus also celebrated the fact God had given them food to survive the coming cold months.