This is the Great Prophet FaDoom.
In the days before the great devastation of Mordheim he was known as Aekold Fastidious Dümbar, a notorious con artist that made his living by selling meteorite insurance to the more cautious/paranoid/gullible of his fellow townsfolk. Most of his profits were either gambled away or lost in poor investments (such as the ill-fated Forest of Loren bypass); this was of little concern to Dümbar, who had never had much of knack for retaining wealth. Besides, he was never going to have to pay out on any of those insurance policies.
And then of course, Mordheim was famously levelled by a meteorite.
Dümbar found this alarming for a variety of reasons. Alarm became sheer terror when an angry mob turned up at his door brandishing a variety of weapons and slightly soiled meteorite insurance policies, demanding that he step outside for some words. With his only routes of escape blocked by the baying horde, Dümbar armed himself with the first thing that came to hand - a rune-encrusted skull mace that he had fished out of the bins along with a load of collectable plates that he had intended to sell on as valuable antiques - and went out to meet his fate.
But fate had something else in store for him. Far from seeking violent retribution, or worse still big cash pay outs on their meteorite insurance, the mob were there to swear fealty to the great prophet that had foretold of their impending doom. Dümbar knew a good grift when he saw it, and raising his skull wand to the heavens he humbly accepted their praise and commanded his disciples to go out and loot the city, smite any unbelievers that might expect some kind of payment off the back of his prophecy, and construct a temple - the Temple of FaDoom.