Dündar Bey was the youngest son of the Kayı Bey Suleyman Shah or Gündüz Alp and the younger brother of Ertuğrul (13th century).
[1][2] At the time of the division of the Kayı tribe, Dündar Bey migrated with his older brother Ertuğrul after the death of their father.
When Osman I decided to attack a small Greek island, Dündar set a trap for him; Dündar rebelled because he thought such an attack would destroy the tribe.
The circumstances surrounding his death are, like many other details of his ill-documented life, disputed.
[1] Dündar Bey has been portrayed in Turkish television series; Kuruluş "Osmancık" [tr] (1988), Diriliş: Ertuğrul (2014—2019) and Kuruluş: Osman (2019—2021).