Pir Husayn (died late 1379) was Emir of Erzincan from 1362 until his death. He was originally the ruler of Karahisar and arrived in Erzincan on 8 June 1362 and succeeded Ahi Ayna, who died on 2–3 July 1362 reportedly as a shaheed (martyr). In Abu Bakr Qutbi's Tarikh-i taqwim, Pir Husayn is mentioned as an emir-zada (lit. 'son of an emir') directly following the statement about Ahi Ayna's demise, hinting at the possibility he was Ahi Ayna's son.^[1]

Pir Husayn's ascendance to the throne was not straightforward as Erzincan was in the midst of a civil war. He "gained independence" on 10 July,^[2] having clashed with emirs opposing to his rule, who eventually fled to Bayburt and Tercan.^[3] On 11 September, he gained control of Bayburt after a 32-day siege.^[2]

Although there is a coin specimen minted in Erzincan for Ala al-Din Ali dating back to 1366, Pir Husayn most likely exercised further autonomy, especially following the temporary political vacuum caused by Ghiyath al-Din Muhammad I's death in 1365. However, there aren't any sufficient accounts of the period until Pir Husayn's death in 1379.^[4]

A copy of Rumi's Masnavi prepared by Muhammad ibn Husayn al-Mawlawi in January–February 1373 probably in Erzincan for "Taj al-Din Shaykh Husayn Beg" is attributed to Pir Husayn's patronage.^[5]