Voss' Raider is a GithyankiNPC encountered in Act One. They cannot be spoken to and are functionally identical to a generic githyanki raider, other than wielding a different weapon.
Voss' Raider accompanies Kith'rak Voss to the player's camp during his clandestine attempt to convince Lae'zel to join his rebellion against Vlaakith. They will fight the party if Lae'zel holds fast in her allegiance to the Lich Queen.