He was the son of Lambert I of Nantes and Adelaide of Lombardy,[a][1] the eldest daughter of Pepin of Italy.
Guy married Ida (Itta, Ita or Itana),[1] daughter of Sico of Benevento.
He acted as arbiter several times for high fees, but only Lothair's successor, the Emperor Louis II, could end the strife.
In 846, he alone succeeded in driving the Saracens out of Latium after their sack of Saint Peter's Basilica in Rome.
By his intervention he secured the Liri Valley, southern Lazio, with Sora and Arpino taken from the count's brother Landenulf of Teano.