Sayyid Fakhr al-Din (Persian: سید فخرالدین) was a Mar'ashi prince, who ruled the region of Rustamdar from 1381 to 1390.
The fortress of Kojur was conquered and made the permanent residence of Fakhr al-Din; the Mar'ashis were now the masters of all of Mazandaran.
The Baduspanids were temporarily ousted from power, until almost a decade later in 1390, when Kamal al-Din I installed Sa'd al-Dawla Tus on the Baduspanid throne in Rustamdar to challenge the Afrasiyabid prince Iskandar-i Shaykhi who accompanied the Turco-Mongol ruler Timur (r. 1370–1405), who intended to conquer Mazandaran.
[3][1] However, Tus secretly corresponded with Iskandar-i Shaykhi, and eventually joined the forces of Timur in 1392.
[5] Tus managed to convince him to spare the Mar'ashi family; they were deported instead, while Iskandar-i Shaykhi was appointed governor of Mazandaran.