As of 2026, Mustafa Üstündağ plays the character of Demirhan Han in the TV series Kuruluş Orhan. Introduced as the powerful leader of the Karesi Emirate, this character is positioned as one of the major rivals of Orhan Bey. Üstündağ's joining the cast was announced in January 2026, and his character is described as the "leader of the seas."