Lastel Longknife was a bandit chief operating in Rethwellan. He had managed to gather several bandit groups into a unified force to sack merchant caravans. Using his own mind magic, Lastel would hide in the caravan as a trusted guard. When the caravan reached a good ambush spot a few days into the trip, he would signal his followers to attack. After killing all the guards, they would take any goods, horses, and women who might be part of the caravan.
He was eventually caught by Tarma and Kethry, who had been hired to do the job. Feeling it was appropriate for his crimes against the women he captured, Kethry locked him into the illusion of a delicate young noblewoman and sent him into the hills to be captured, tortured and most likely killed by the remains of his band. The story was inaccurately told by the minstrel Leslac in the song "Threes."
Lastel survived and escaped. He eventually made his way to Oberdorn, where he hunted up a washed out magician to help him with his curse. Since Kethry had sealed the spell with both her signature glyph and the glyph for justice, no legitimate sorcerer would break the illusion. The magician he found did not have the power to break Kethry's spell. In stead he summoned a demon with a grudge against Kethry. His non-specific summoning brought forth Thalhkarsh, who tortured and ate the magician, then transformed Lastel, turning him into the woman he appeared to be.
Lastel struck a bargain with the demon, offering to lure Tarma and Kethry to him for revenge. In return, Lastel wants his original body back. When he succeeds, and Tarma and Kethry have been captured, Thalhkarsh gives him Kethry's body instead. Thalhkarsh has plans to make the now mage-gifted Lastel his High Priestess. Lastel, however, is slowly sliding into madness.
During the final battle with Thalhkarsh, Warrl broke the neck of Lastel's body, with Kethry trapped inside. In those dying moments, spells were shattered and Nemor, a local archpriest, reversed most of the transformations. Lastel was a man once more and back in his rightful body, but died in the process.