In Turkey, a commander or chief officer. It is used also as a title of respect.

or aga = Turkish word for elder brother, chief, or master; in Ottoman usage, the title of a high-ranking military official, as in Janissary Aga, head of the Janissary corps.

title for a civil or military leader (especially in Turkey)

a military or civilian ruler

Agha (or Aga) (modern Turkish: Ağa, Bosnian: Aga, Persian: آغا ) from Turkish Agha 'big brother' , ‘leader’, ‘ruler’. As a title for a civil or military officer, or often part of such title, it was placed after the name of certain military functionaries. At the same time some Court functionaries were entitled to the agha title.