William of Hirsau was a 11th-century Benedictine abbot and influential monastic reformer from Bavaria. Serving as the leader of Hirsau Abbey, he spearheaded the Hirsau Reforms, which implemented Cluniac-style discipline across numerous German monasteries. A scholar of the quadrivium, he was highly regarded for his expertise in music, astronomy, and mathematics. Beyond his monastic leadership, he was a significant supporter of the papacy during the Investiture Controversy, working to secure the independence of religious institutions from secular control.