DA4: Zugzul the One

The Afridhi are a fiercely monotheistic people, as indicated by the epithet for their god.

Zugzul's name is derived from "Zug" (meaning "ice" or "cold") and "Zul" (meaning "fire"), also reflecting his male and female aspects.

Zugzul the One.  Illustration by Dave Dorman.

DA4 "The Duchy of Ten" was published after the D&D Master Set (1985) and Immortals Set (1986) rules, and so refers to Zugzul as an immortal:

Though the Afridhi worship Zugzul as a god, he is in fact something less than that. At one time a mortal man, he has long since passed from the ken of lesser folk to become one of the Immortals.  These superbeings are described in part in the D&D® Master Set Rules and in full in the D&D® Immortals Set Rules.  If you have those rules, you may want to use the material found in them to enrich play of this adventure.

Zugzul serves the Sphere of Energy, which is closely related to the element of fire.  His purpose is to create more energy and activity.  Energy is highly active, dynamic, and excited.  It seeks to alter and transform things, consuming Matter, slowing Time, and exciting Thought to release more Energy.  Energy represents disorder, uniqueness, and the Chaotic alignment.

DA4 "The Duchy of Ten" (1987)

Given his description as an immortal, it's surprising that Zugzul was not mentioned in the Codex of the Immortals (1992) by Aaron Allston (Book One of the "Wrath of the Immortals").

Fan publications have associated Zugzul with Corona, an immortal described as a secret ally of Thanatos in GAZ2 "The Emirates of Ylaruam" (1987).