It is generally believed that it was here that William first became friends with Ulrich of Zell (later distinguished as a Cluniac reformer and a saint), a friendship which lasted to the end of his life.

He immediately took over the management of the monastery, but refused to accept the abbatial benediction till after the death of his unjustly deposed predecessor in 1071.

A writ of Emperor Henry IV, probably drafted shortly after 1070, although it created the important link between the abbey and the monarchy, nevertheless largely confirmed the status of Hirsau as a private monastery of the counts.

Henry IV immediately put the monastic community under his own protection, although Hirsau was not made an imperial abbey directly answerable to the monarch (reichsunmittelbar).

Under William's abbacy, Hirschau reached the zenith of its glory and, despite the unusually strict monastic discipline which he introduced from Cluny, the number of priest-monks increased from 15 to 150.

As the monastery, dedicated to Saint Aurelius, was cramped, over-crowded and subject to flooding, He built a new monastic complex on the opposite side of the Nagold.

On this occasion he became acquainted with Pope Gregory VII, with whose efforts towards reforms he was in deep sympathy and whom he afterwards strongly supported in the Investiture Controversy against Henry IV.

Parallel with these developments he found it necessary, in order to bring under some sort of control the great numbers of laymen flocking to Hirsau, to create the institution of the conversi in the German Benedictine monasteries.

The spread of the Hirsau Reforms was directly related to the reputation William had acquired through the ecclesio-political propaganda of the Investiture Controversy, as the main support of Pope Gregory's faction in Germany and in Swabia.

Among other things, the tenacity of the Gregorian party in south-west Germany was due to him, quite apart from the reputation of Hirsau Abbey among ecclesiastical reformers.