Thief of fire? Fire summon that autocasts darkness (make him see in the dark, give him a terrible precision rating, to stop some of your more obvious fire evocations), has awe and a fire weapon? Giant (Titan)sized (modify the smith god or the cyclops art)... basically an army killer, not that fire needs more of those really. Would need specific counters, but the idea of a giant that autocasts darkness and has some obvious ways to deal with undead apeals to me.
"In the days when the All-god (I can't be bothered to attempt spelling the other version
, Pankrater?) controlled the flame many heroes attempted to steal this source of power. All were foiled and many were put to death, but the most powerful were imprisoned within the very source of fire itself. Furthermore they were cursed, even when trapped within the source of all fire they were surrounded by darkeness. A firemage must use a great amount of magic to free these titans from their prisons but the very fact that they have survived millenia of eternal heat and darkness is a testemant to their physical and mental might" Hmm sounds more like a pretender chassis, it will probably have to be toned down a little to see use."
Hey I like spewing forth half formed ideas... I really should learn to mod