Gavin Guile was the oldest of the three Guile brothers, son of Andross and Felia Guile. He and Dazen were close during childhood but grew apart Andross began to show favor to Gavin, and the tension between them only increased when he became Prism-elect. Gavin is Zymun's true father and is believed to be father of Kip Guile. Gavin and Dazen's younger brother, and therefore the youngest of the three, was Sevastian Guile, who was killed by a blue wight when he was eight. Gavin became Prism, but in spite of his great magical prowess was still bound to the Spectrum. He wanted to become Promachos, at the direction of his father. He was secretly captured by his brother, Dazen, during the (False) Prism's War.

Despite Gavin being older than Dazen by three years, the two of them were often mistaken for twins due to their incredible similarity in appearance and mannerisms. This made it all the easier for Dazen to convince the entirety of the Seven Satrapies that he was his brother. Any differences in his behaviour were written off as being from the trauma of the war and having to kill his brother.

The Prism's/False Prism's WarEdit

In order to become Promachos, Andross and Gavin needed to incite a war. Tensions were already high between the brothers Guile after Dazen revealed to his brother that he had begun to be able to split light, but it all came to a breaking point when Gavin betrayed Dazen's elopement with Karris. When Karris went to her and Dazen's meeting place she found not Dazen waiting for her but her father who took her away on a boat to Gavin. Meanwhile, Dazen showed up at the Whiteoak estate only to discover an ambush set up by Karris' brothers. They had locked the gates and started a bonfire, assuming that because of the night and the flames none of his colors would be usable. In the end, it was revealed that Dazen could draft Red and Sub-red. He killed the brothers and left the house locked to burn, not knowing how many people were inside. Karris and the rest of the world believed that Dazen had attacked the estate himself in a fit of vengeful rage, and Dazen fleeing was enough to start a war. Dazen gained followers as he emerged as a full spectrum polychrome could split light - he was also a rightful Prism.  

Gavin also ordered massacres and bought off one of Dazen's generals to commit a massacre. He did this to fire up the war and make sure Dazen did not surrender, because he would have to give up his title of Promachos. At the battle the final battle of Sundered Rock, Dazen defeated Gavin, imprisoned him and then took his place, so he would not have to give concessions to all of his immoral allies. The world then believed Dazen dead and Gavin victorious.

Blood MirrorEdit

In reality Gavin died in battle of Sundered Rock, when Dazen used black luxin to kill him. Gavin in first books was only Dazen hallucinations.