Mehmed Ağa, known as Sedefkâr Mehmed, was Chief Imperial Architect of the Ottoman court (mi'mārbaşı) from 1606/1015 AH to circa 1622/1030 AH. His most famous work is the Sultan Ahmed Complex in Istanbul.

According to his biography, Mehmed Ağa came to Istanbul in 1562-3/970 AH as a recruit of the devşirme, or Ottoman levy on Christian boys from the villages of the Balkans and Central Anatolia. His first paid job was in the corps of gardeners (bostāncı), and then he trained as a worker of mother-of-pearl inlay (sedefkār), which ushered him into the world of architecture. It is from this occupation that he took his nickname.

He studied architecture under Mimar Sinan, the most famous of Ottoman chief imperial architects, and then under Sinan's successors Davud Ağa and Dalgıç Ahmet Aga. His first major appointment was as Water Channel Superintendent (ṣū nāẓırı) of Istanbul, which he received in 1597/1006 AH. He held this post until 1606/1015 AH, when he became Chief Imperial Architect.

Sources:

Çobanoğlu, Ahmet Vefa. "MEHMED AĞA, Sedefkâr." TDV İslâm Ansiklopedisi. Available online at: https://islamansiklopedisi.org.tr/mehmed-aga-sedefkar [Accessed September 23, 2019]. 

Cafer Efendi. Risāle-i Mi‘māriyye. An Early-Seventeenth-Century Ottoman Treatise on Architecture. Translated and annotated by Howard Crane, p. 7-15. Leiden: Brill, 1987.

Necipoğlu, Gülru. The Age of Sinan: Architectural Culture in the Ottoman Empire, p. 154 and Appendix 4.5, p. 565. London: Reaktion Books, 2005.