These ancient, undead warriors are charged to eternally guard Nosgoth's ancient shrines, and challenge any intruders. Some Thralls exhale projectiles at Raziel, and will strive to keep their distance, but will attack if cornered. Thralls sometimes carry emblem-keys which Raziel needs in order to progress.
Historically, Thralls were slaves in the Viking age of Scandinavia (and the root of the word "enthrall").
Similar "Thrall" enemies, arguably inspired by the same concept would later appear in Crystal Dynamics' Tomb Raider: Underworld, where 'Thralls' were undead enemies raised by the liquid "etir". These thralls had a notably similar appearance to Legacy of Kain thralls; with the "Viking Thralls" in that game sharing particular traits with the Swordsmen thralls of Soul Reaver 2.