Muawiyah also encouraged peaceful coexistence with the Christian communities of Syria, granting his reign with "peace and prosperity for Christians and Arabs alike", and one of his closest advisers was Sarjun, the father of John of Damascus. At the same time, he waged unceasing war against the Byzantine Roman Empire. During his reign, Rhodes and Crete were occupied, and several assaults were launched against Constantinople. After their failure, and faced with a large-scale Christian uprising in the form of the Mardaites, Muawiyah concluded a peace with Byzantium. Muawiyah also oversaw military expansion in North Africa (the foundation of Kairouan) and in Central Asia (the conquest of Kabul, Bukhara, and Samarkand).
Try to answer this question if possible (otherwise reply "unanswerable"): Who was Muawiyah's least close adviser?
unanswerable