Anno was responsible for the miniature. you can probably still get this model. a few months ago I asked anno if they are still available and he promptly replied… although I havent seen him much around here lately.
So you need a good story to explain the hugeness of Zargod!
That's actually quite easy with the powers of Chaos. They did the same with Nicodemus, an old Mordheim character. Apparently the figure was a test model by a new sculptor but it was too big. Because it was too cool to not bring out they decided he was cursed by a Daemon (he had one wish and wished to be the 'biggest' sorcerer in the world!) explaining why he was so big. :)