Klæl is the primordial opposite of Bhelliom. Because Bhelliom is a blue spirit of seemingly mild and amiable temperament, Klæl is thus a red spirit who seems to crave destruction and bloodshed. The two beings seem to otherwise be perfectly equal in strength and ability. Like all other spirits, Klæl is androgenous, although the Church Knights and their allies call it a "he".
Klæl appears whenever Bhelliom forges a new world, at which point the two engage in combat to decide who controls it. The fight only ends when either one or the other cedes the world to the victor, or when the world is obliterated. In one special case (when Bhelliom didn't pay attention and was confined in an iron deposit), Klæl technically gained possession of the world by default. The victory was short-lived, however, as the Elder Gods of Styricum banded together to cast him out.
In The Hidden City, Cyrgon orders Cyzada to undo the spell keeping Klæl out, allowing him to return and do battle with Sparhawk and his allies. He causes a great deal of problems across Tamuli until he is defeated when he chooses Cyrgon as his champion. Sparhawk (or, more accurately, Anakha), acting as Bhelliom's champion, confronts and defeats Cyrgon using the same strike with which he defeated Martel. As a result, Klæl loses his customary "contest" with Bhelliom and so is permanently banished from their world.
When in Sparhawk's world (or at least while under Cyrgon's control), he appears as a colossal, winged, clawed monster surrounded by fire and lightning, but his "true" form is a red, vaguely humanoid being of light. He can summon armies of aliens from Arcera and presumably his other controlled planets to battle by his side (and often in his stead).