The kizlar agha, formally the agha of the House of Felicity, was the head of the eunuchs who guarded the Ottoman Imperial Harem in Constantinople.

A eunuch is a male who has been castrated. Throughout history, castration often served a specific social function. The earliest records for intentional castration to produce eunuchs are from the Sumerian city of Lagash in the 2nd millennium BCE. Over the millennia since, they have performed a wide variety of functions in many different cultures: courtiers or equivalent domestics, for espionage or clandestine operations, castrato singers, concubines or sexual partners, religious specialists, soldiers, royal guards, government officials, and guardians of women or harem servants.