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 Colour 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."

Despite both of his parents being famed for their attractiveness, Zymun is not a good-looking man, nor does he particularly resemble his parents. He has blue eyes, a large, hooked, aquiline nose, a wide mouth, light brown skin (described as the skin colour typical of Atashians,) dark eyes, and dark, curly, unruly hair. His teeth however, as 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 full-spectrum polychrome, and is the current 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 a special knife (possibly a Blinder's Knife,) and Kip later sees Zymun slipped 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.