Classically,
夫子 was the highest respectful address for a learned man — most famously
孔夫子 (Kǒng Fūzǐ, Master Kong = Confucius), from which Western 'Confucius' is Latinized. By extension
孟夫子 = Mencius,
朱夫子 = Zhu Xi. Hong Kong's beloved comic 《
老夫子》 (Old Master Q) keeps the term in pop-culture circulation today.