The Elemental lords are the rulers of the Elemental Planes, and are part of the Ancient universe. The four Elemental lords are Acwalandar, the Lord of Water; Shalwend, the Lord of Air; Pyrannaste, the Lord of Fire; and Gralkor, the Lord of Earth.
It should also be noted that in the "To Kill a Hero" scenario; there is a character called Tamar the Wanderer, self-proclaimed to be the Elemental Lord of Air. Even though this might be a simple disguise, the later mentions of Elemental Lords in the "Master of the Elements" campaign (where they are never referred to by names), implies that there might be a continuity error or several Elemental Lords.