Zymun is the illegitimate son of Gavin Guile and Karris White Oak.
Based on his actions and other characters' reactions to him, (such as Liv, the Blackguards, and even the Color Prince,) it is likely that Zymun is a sociopath; having little or no capacity to feel compassion or most other normal emotions. He appears to be motivated solely by lust and greed: for power, for wealth, for women, and for whatever else he wants. He is also extremely narcissistic and a consummate sadist. In The Broken Eye, when a pirate ship is about to take Zymun aboard after his dinghy sinks, he is giddy at the thought of being able to kill people without consequences. When the pirates bring him on board their ship, he decides to start killing people in order to be taken seriously in negotiating his passage on the ship, despite being fully aware that they could be reasoned with peacefully (he says as much to himself.)
Liv says that: "he was a lizard beneath [his charm. There was something wrong with him. Something thin, an essential shallowness." Likewise, the Colour Prince says that "there is no human warmth in him." Kip remarks that Zymun is "pure reptile." During a conversation between Andross and Kip, they agree that Zymun "lacks any human decency or emotion, other than ambition."
Zymun is described as very handsome by several characters, including Liv, Teia and Karris. He has blue eyes, an aquiline nose, light brown skin (described as the skin colour typical of Atashians,) dark eyes, and dark, curly, unruly hair. His teeth are described as "perfect bright white [teeth]."
His full name is technically Zymun Guile, but he does not use his surname since he is an unacknowledged bastard. The first time he introduces himself and explains his parentage, (to his half-brother, Kip Guile,) he refers to himself as Zymun White Oak.
Zymun is a six color polychrome by the time he fought for the Color Prince. He is the former Prism-elect.
Before coming to the Chromeria, Zymun served Rask Garadul and the Colour Prince, and took part in the massacre of Rekton. During the massacre, he showed his sadism and took delight in acts of cruelty towards the townsfolk as well as animals in Rekton.
Before the Battle Of Garriston, the Colour Prince entrusts Zymun with the Blinder's Knife and Kip later sees Zymun slip onto the last ship evacuating people from the city. Just as Kip makes it to the barge, Zymun stabs Gavin, but Kips tackles him off the deck and into the water, breaking his nose in the process, and proceeds to punch him as hard and as fast as he can while in the water. Seeing sharks nearby, Zymun retreats and swims for shore, and Kip takes possession of the knife, which Zymun had let go of during their struggle and Kip had grabbed it. Zymun eventually makes it to shore and rejoins the Colour Prince's army.
After the Battle of Garriston Zymun becomes the tutor of the newly arrived Liv Danavis, introducing her to the ways of camp life, under instruction from the Colour Prince. The two soon become rivals vying for the Colour Princes favor and after the siege of Idoss become lovers. Liv soon discovers his true nature as a Sociopath with no feelings towards anyone.
Zymun is then ordered to lead a strike force of 20 men to infiltrate the tower fort of Ruic Head for the Colour Princes army in preparation for the Battle of Ru. Zymun successfully captures the fort but almost immediately retreats due to the Blackguard assault led by Tia and Ironfist. In a scuffle in a hallway Zymun almost kills Tia however his pistol misfires, having no chance of victory Zymun flees from the advancing Blackguards.
Having failed the Colour Prince twice, Zymun realises he is no longer welcome in the Colour Prince's army so he decides to head to the Chromeria to seek the aid of his paternal grandfather, Andross Guile. On his way to Big Jasper via a rowboat he stops at a beach where many corpses from the Battle of Ru have floated to shore. Deciding to loot the bodies he stumbles upon an unconcious Kip, who awakens and is then taken prisoner. After taking Kip prisoner he reveals the pistol he found on the beach that he used to subdue Kip was in fact empty. Laughing at this he then directs a chained and blindfolded Kip to row them to Big Jasper, revealing to his prisoner that they are in fact brothers.