Borlath was the eldest son of the Red King. A brutal, sadistic tyrant, he had the twin endowments of pyrokinetics, the ability to make and control fire, and hypnotism, as discovered in Leopards' Gold when he brought Olga into a trance to stop her hysterical telekinetic rampage after Lilith's abrupt departure from the castle.
Borlath's favourite pastime was torture, and he used this to pervert the originally good nature of the blue boa so that its embrace would kill. Borlath's sister Guanhamara used her magic to partially undo this, so that the boa's hug would only turn its victims invisible.
After the death of Queen Berenice and departure of the Red King, Count Harken Badlock married Borlath's sister Lilith and she, Borlath and three more of their siblings were given free rein to use their powers for evil. Their five good-natured siblings fled the Red Castle, and Borlath's eldest younger brother Amadis led his followers to an island where they constructed a beautiful castle. Amadis married Elin and they had four sons, but Borlath eventually discovered the castle and tried to take it by force with an army of mercenaries. Amadis used his power to recruit the birds and beasts of the island to his side, and Borlath's army was harassed by birds while rats ate all of their supplies. Borlath had wanted to capture the castle intact, but Amadis' resistance eventually infuriated him so much that he summoned a great fire which killed almost everyone inside, including Amadis and his and Borlath's youngest sister, Amoret, who had also taken refuge there. Mathonwy, a Welsh magician who was friends with the Red King, sensed the disaster from afar and sent a magical snowstorm to douse the flames, which had the effect of turning the castle walls to glass and giving it its name: the Castle of Mirrors. Seeing their own reflections, Borlath's army fled in fear. The only survivor of their assault was Amadis and Elin's youngest son, an albino named Owain.
Borlath married a woman named Shushilla, and The Bloor Family are among their descendants. After The Fire of the Eighteenth Century, the Bloor family founded Bloor's Academy on the grounds of the Red Castle, and one of them, Bertram Babington Bloor, discovered Borlath's cloak and pin inside his tomb there. Ezekiel Bloor attempted to use the cloak and pin as props in a necromantic ritual to bring Borlath back to life, but the heart he was working with actually belonged to Berenice and he only succeeded in resurrecting the queen in the body of Borlath's warhorse Hamaran.