William II, the Norman king of Sicily, has become known as William the Good because of his policy of clemency and justice toward the towns and the barons, in contrast with his father, William I the Bad.
After the regency of his mother, Margaret of Navarre, had ended, William II at first continued his father's policy of friendship with Pope Alexander III and with Constantinople’s emperor, Manuel I Comnenus.
In 1172, however, the emperor thwarted the proposed marriage of William to Manuel's daughter Maria, and William immediately turned against the Greeks.
In 1177 he concluded a truce with his father's old enemy, the German king Frederick I Barbarossa, who had been defeated by the Lombard League at Legnano in 1176 and no longer seemed dangerous to Sicily.
Also in 1177, on February 13, William had married Joan, daughter of King Henry II of England.
After the death of Pope Alexander III in 1181, William had felt freer to exploit disorders in Constantinople’s empire, and had sought even closer relations with German emperor Frederick I Barbarossa.
William agreed that his aunt Constance should marry Frederick's son, the future Henry VI; because William's own marriage is childless, this betrothal, formally arranged on October 29, 1184, gives Henry a strong claim to the Sicilian succession, an arrangement disliked by the Norman national party.
In June 1185, William commences a great campaign against the Eastern Roman Empire.
In the same year, construction begins on the cathedral at Palermo, erected in 1185 by Walter Ophamil (or Walter of the Mill), the Anglo-Norman archbishop of Palermo and King William II's minister, on the area of an earlier Byzantine basilica.