I don't remember when he was introduced (possibly 6th Ed?), but the story was that Vilitch was the son of a chieftain (Norscan, I believe). Vilitch had an older brother, who was big, strong and all the other things a barbarian warlord need to be. Vilitch, on the other hand, was a diminutive mutant, a disgrace in his fathers eyes, abused by his older brother and treated as a serf. Mind you, Vilitch did study under the village Shaman, where he learned of the Chaos Gods, and so he would pray to Tzeentch to change his fate, so that Vilitch could have his brothers size and strength.
Tzeentch, being Tzeentch, obliged Vilitch by fusing him and his brother together, mindwiping the sibling and leaving the sorcerous Vilitch perched on top of his new meat-puppet mount, like an irredemably evil Chaos-version of Master Blaster. Vilitch promptly used his newfound strength and power to massacre those who had abused him, before setting off into the Chaos Wastes to form his own warband.
For the record, I always prefered the original "evil puppeteer" take on the character over the "devil-on-the-shoulder" model you linked:
http://1.bp.blogspot.com/_9bulPY0yh_...00/Vilitch.JPG
http://1.bp.blogspot.com/-HS4uKtwV4V..._7980+1000.jpg
Last edited by Andnore; 19-05-2016 at 09:22.
He was introduced in the 7th edition Chaos Warriors Book. That, the 8th and the End-Times stuff are all you'll find about him most likely.
"If more of us valued food and cheer and song above hoarded gold, it would be a merrier world."
-Thorin Oakenshield, The Hobbit
Since the End Times, Tzeentch decided to make his elder brother the controlling force of their union, while Vilitch is reduced to a drooling automaton. So this model might as well be called "Thomin".