Following the conquest of Constantinople in 1453, Ottoman Sultan Mehmed the Conqueror took this title, meaning "Caesar of Rome".

Qaisar (قیصر) or Kaysar evolved to mean "King" or "Ruler".

"Kayesrar" is a variant spelling of (or Qaisar ), a title and name with deep roots in Roman, Persian, and Islamic history . It is the Arabic and Persian adaptation of the Roman imperial title Caesar , evolving through history from a family name to a symbol of absolute power and majesty. 1. Etymology and Linguistic Evolution

Throughout history, the title has been adopted by various powerful dynasties to claim the legacy of Rome: