Yahya Efendi was an Ottoman religious scholar, a Sufi master, and a poet during the reign of Kanûnî Sultan Süleyman and Selim II. Yahya’s father Ömer Efendi was a town judge in Trabzon where Yahya Efendi and Süleyman I were born one after another in one week in 1494. Because Yahya’s mother was Süleyman’s wet-nurse, the two established close relations from childhood. Yahya for the same reason enjoyed a connection with the Ottoman court. Yahya left Trabzon for Constantinople to continue his formal education and fulfill his traditionally-forty-day solitary retreat, or çile. Afterwards, Yahya completed his education under Zenbilli Ali Efendi’s supervision. As a teacher, Yahya went by the name “Molla Sheikhzade” at Sahn-ı Seman medrese, the highest educational facility built in 15th century. Yahya Efendi’s formal education was primarily religious. However, being Süleyman’s milk brother, he had good relations with literary circles in Constantinople. He wrote poetry and prose, and his prose included mostly instructional Sufi parables. His magnum opus, titled simply Divan, was primarily written in verse. During his lifetime, Yahya Efendi was recognized as a leading light of 16th century Ottoman society. He fell from that position, however, after criticizing Süleyman’s attitude toward his son Şehzade Mustafa’s death. Süleyman sent Yahya away on a humble pension. Yahya continued his criticism of high officials like Rüstem Pasha and Sokullu Mehmet Pasha. He spent the rest of his life in Beşiktaş, where he played a major role in the conversion of non-Muslims and giving sermons. He was buried around 1571 in Beşiktaş. Yahya Efendi underwent a significant transformation in his career as a medrese teacher to a Sufi sheikh. This paper illustrates that transformation through analysis of Yahya Efendi’s conversion narratives, social composition, and his mobility within the bounds of his patronage under Süleyman. Yahya’s transformation naturally had political aspects as well, clearly visible in how Yahya’s opinions of Ottoman bureaucracy became entirely negative. I trace these developments with a prosopographical approach and analyze the relations between Yahya Efendi, Süleyman, Şehzade Mustafa, and Selim II. This approach helps us to observe the negotiation tools that Yahya Efendi used to envision Ottoman sultans, while endorsing—or criticizing—Ottoman internal and foreign policies.