Akyazılı Baba (Ak Yazılı Sultan) was an early-16th-century Bektashi leader regarded as the spiritual heir of Otman Baba and the kutb al-aktab of his time. His tekke complex near Obrochishte, near Balchik, developed under Süleyman I and is famed for its rigorously heptagonal architecture; the fully preserved türbe, about 12 m high, is reputedly the tallest such sanctuary in the Balkans. From the late 19th century it became a bi-ritual Muslim-Christian sanctuary, locally venerated also as the tomb of St. Athanasius. (Sources: Historical Museum of Balchik; Yelis Erolova, Contemporary Development of the Akyazili Baba Tekke / St. Athanasius in Bulgaria, Folklore/Sator 18, 2017; Belleten/TTK 1967.)