Vermuellen was a Koviri Prince, duke of Creyden and the head of intelligence in Kovir. He married Gaudemunda Thyssen who bore him a son, Guiscard Vermuellen.
In Wiedźmin: Gra Wyobraźni PnP RPG
According to the Wiedźmin: Gra Wyobraźni, Koviri prince Aristide Vermuellen, duke of Creyden, was head of intelligence in Kovir. His secret service cooperate with dvarvish banks of Vivaldi and Cianfanelli.