Too tempted by the Month of Marsh challenge (
http://forum.oldhammer.org.uk/viewtopic.php?f=29&t=7786) I have converted up my own Fimir. I was cunning enough to incorporate him into my army by making him double up as a Nurgle Ogre.
He turned out interesting enough I thought he deserved his own little backstory. Something like:
"The Daemon had fooled him, he knew that now. The quest that had taken him from the misty marsh of Albion to the craggy wilderness beyond the sea had been a ruse, he was sure of it. It had not taken long before they were all lost in the mountains, unable even to find their way back. The natives of these lands were a peculiar sort; short but fierce, many of them more than a match for Crounach and his Fimm Warriors. They had been cornered in a gully and the bearded ones had made short work of his retinue, hacking them down to a man. Not him though, and when he had laid twenty of them low they had ceased to fight and laid down their arms. Another of their sort came forth, but not a warrior; a priest or a shaman of some sort by the looks of his garments. He had spoken a few words in his guttural language and bid Crounach to follow.
---
On the walls of their mountain abode he had seen the old mural of the object of his quest. So it was true after all, the daemon had not lied. The small, stout men had pointed to it, then pointed to Crounach, gesticulated wildly and babbled excitedly. Then they had taken him to the depths of their lair, where slaves chained to bellows had been stoking roaring furnaces. In that dark pit the half-men crafted him a suit of armour like their own and their shaman had chanted over it in their strange tongue and held his arms aloft whilst his eyes rolled back in his head.
---
The recollections had long since started to blend into each other and the memories came and went. Memories of a foggy place he used to call home once, but not sure where, or when. Memories of his band of dwarven followers, but they were also long gone now. He had carried on with renewed vigour after finding the monolith that had the object of his quest inscribed in crumbling symbols and fading paint. Or was it the witch with the two headed wolf that had directed him upon the path again? He could barely make heads or tails of it anymore, it felt like his brain was slowly rotting away in these stinking badlands. Just a bit further, he kept telling himself as he cast a backwards glance at his motley followers. Just a bit further..."