Bishop of Vercelli from 924. Of a distinguished Lombard family, son of Viscount Aldegarius, he was also grand chancellor to Hugh of Provence, king of Italy. De pressuris ecclesiasticis (about 940) is his earliest major work, on refutation of charges against clergy, filling of clerical posts especially bishoprics, and lay seizure of church property after a bishop’s death. He also wrote Commentary on the Epistles of Paul, Letters and Sermons, Canones statutaque Vercellensis ecclesiae, and Polipticum on moral philosophy. He should not be confused with Atto of Milan (d.1085/6), who wrote Breviarium, which was the basis for Gregorian reforms.