WILLIAM I. (d. 1166), king of Sicily, son of King Roger II. by Elvira of Castile, succeeded in 1154. His title "the Bad" probably expresses the bias of the historian Falcandus and the baronial class against the king and the official class by whom he was guided. William was far inferior in character and energy to his father, however, and the real power in the kingdom was at first exercised by Maio of Bari, whose title ammiratus ammira torum was the highest in the realm. Maio continued Roger's policy of excluding the nobles from the administration, and sought also to curtail the liberties of the towns. The barons were encouraged to revolt by Pope Adrian IV., whose recogni tion William had not yet sought, by the emperor Manuel and the emperor Frederick II. At the end of 1155 Greek troops re covered Bari and began to besiege Brindisi.
William, however, destroyed the Greek fleet and army at Brin disi (May 28, 1156) and recovered Bari. Adrian came to terms at Benevento (June 18, 1156), abandoned the rebels and con firmed William as king, and in 1158 peace was made with the Greeks. These diplomatic successes were probably due to Maio;
on the other hand, the African dominions were lost to the Almohads (1156-116o). The policy of the minister led to a general conspiracy, and in November 116o he was murdered in Palermo by Matthew Bonello, leader of the Sicilian nobles. For a while the king was in the hands of the conspirators, but the people and the army rallied round him ; he recovered power, crushed the Sicilian rebels, and in a short campaign reduced the rest of the Regno. Thus freed from feudal revolts, William con fided the government to men trained in Maio's school, such as the grand notary, Matthew d'Agelio. He was the champion of the true pope against the emperor, and Alexander III. was installed in the Lateran in November 1165 by a guard of Normans. Wil liam died on May 7, 1166.