Vilhelm is fighter-assassin hired by an anti-magic faction in Athkatla during the Baldur's Gate II: Shadows of Amn campaign. He only appears in the Planar Sphere during the final phase of the Mage Stronghold quest.
Vilhelm is accompanied by six others, including three fighter-assassins named Sergeant Natula, Tyrian, and Jalin Tix, along with Mahar (a Monk), Alnarow (a Thief), and Sorsha (a Druid).