William left
Normandy around 1053 with his elder half-brother
Geoffrey and full brother
Mauger. He participated in the
Battle of Civitate in the years of his arrival and was received cordially by his half-brother
Humphrey, the reigning
count of Apulia. In 1055, he distinguished himself in the taking of the castle of San Nicandro (today
San Licandro) close to
Eboli, which formed the nucleus of his county of the
Principato, with which he was invested by Humphrey in 1055. In 1058, he married Maria, the daughter of
Guy, Duke of Sorrento and brother of
Guaimar IV of Salerno. He inherited all Guy's lands in the
principality of Salerno and fought with Guaimar's successor,
Gisulf II, whose lands he ate away at until little was left but Salerno itself. He also inherited the
Capitanate from Mauger, who died between 1054 and 1060. That last possession he gave to Geoffrey, out of fraternal love,
Malaterra informs us. He invited his landless youngest brother
Roger to join him, promising him half of all he owned, save his wife and children. He aided Roger against their elder brother
Robert Guiscard, who had succeeded Humphrey, and gave him the castle of
Scalea, at
Catanzaro. He fought against Robert later when Robert came to the aid of Gisulf in order to receive in marriage Gisulf's sister
Sichelgaita. In 1067, the Council of
Melfi excommunicated him, along with Turgis de Rota and Guimond de Moulins, for stealing property from the church of
Alfano I, Archbishop of Salerno. Later that year, he travelled to Salerno to reconcile with
Pope Alexander II. ,
Venosa According to some sources, he died in 1080, though others have him living into the twelfth century (to 1104, 1113, or 1117) and participating in the Guiscard's
Byzantine campaigns and being present at the
Battle of Durazzo, October 1081. He was buried in the
church of the Santissima Trinità in
Venosa. ==Marriage and issue==