His friendship with Borric ended when they competed for the hand of Catherine, with Borric eventually winning her and taking her to Crydee. When Guy first came to be Duke of Bas-Tyra, this event caused him to take to wearing only black as a badge of sorts, earning him the name Black Guy.
When King Rodric IV was coronated, Guy was candidate to become King's Regent but Borric, Prince Erland and Duke Caldric objected; he lost the position to Caldric. However he continued to have influence over the King and perhaps hoped to be his successor, after the King's relationships with Erland were in bad terms.
During the Riftwar, Guy, as an advisor of the King, did not encourage him to give his order to muster the Armies of the West. It was supposed that he intended to let the West suffer a little, until the issue was in doubt, and then to come with the Armies of the East as a savior.
King Rodric IV named Guy Viceroy of Krondor. He asked for the hand of Princess Anita in marriage. When he was denied, he imprisoned Prince Erland (who later died because of it).
He led his troops down to the Vale of Dreams during a mini-war with Great Kesh soon after Arutha arrived aiming to secure troops to defend Crydee. After Rodric IV died, and Lyam conDoin was named heir, Guy fled the city, going north. Lyam marked him a traitor and ordered his execution if he returned.
In the meantime, Guy, Amos Trask and Armand de Sevigny departed the Kingdom and made for the Keshian Confederacy. They were pursued by pirates, then later attacked by goblins who killed most of their crew and ultimately delivered them to a group of moredhel. The moredhel were intercepted by a group of Armengarians. Guy travelled to Armengar and trained them in modern warfare. He then became the Protector of Armengar.
When Prince Arutha conDoin arrived at Armengar, Guy immediately agreed to help him in his cause. But he was stopped when Murmandamus's army besieged Armengar, and Guy was forced to flee to the mountains.
After the Siege of Armengar, the survivors fled to Highcastle, where they once again tried to hold Murmandamus's army. Again they fled, this time to Sethanon, where Murmandamus stood his final assault. Here Murmandamus was defeated and peace was, for a time, restored.
After the battle of Sethanon, Guy was named Duke of Rillanon and First Advisor to the King.