The conflict with Habsburg ended in 1534 when both dukes reached an agreement with Ferdinand I in Linz. William then supported Charles V in his war against the Schmalkaldic League in 1546. William’s chancellor for 35 years was the forceful Leonhard von Eck.
William was a significant collector and commissioner of art. Among other works he commissioned an important suite of paintings from various artists, including the Battle of Issus by Albrecht Altdorfer. This, like most of William’s collection, is now housed in the Alte Pinakothek in Munich. With his order to expand the Neuveste with the so-called Rundstubenbau and to set up the first Court Garden began the history of the Munich Residence as a representative palace.
To the history cycle of the garden pavilion belonged Albrecht Altdorfer’s painting. In 1546 he ordered to upgrade Dachau Palace from a Gothic ruin into a renaissance palace. In 1523 with the appointment of Ludwig Senfl began the rise of the Bavarian State Orchestra.
On 23 April 1516, before a committee consisting of gentry and knights in Ingolstadt, he issued his famous purity regulation for the brewing of Bavarian Beer, stating that only barley, hops, and water could be used. This regulation remained in force until it was abolished as a binding obligation in 1986 by Paneuropean regulations of the European Union.
William died in 1550 in Munich and was succeeded by his son Albert. He is buried in the Frauenkirche in Munich.