Baudros

"It was going to die there, in this foul and miserable place, the burial ground of some forsaken and wicked people who had long ceased to befoul the world. From the cairns issued a dark mist, and that mist coalesced into a form something like a man, but far bigger, indistinct, and ill-proportioned. The dragon's blood gave it form. Three green eyes burned deep inside it, and a voice issued that was barely distinguishable from the cold hiss of the mountain winds. Its words were obscure, but its meanings were clear. It was without a body, sustained here only by ancient hate of those who had worshiped it. The dragon was going to die there if some supernatural force did not intercede. And between them, they were making a pact."

- The Tale of Baudros

Baurdos, the dragon formerly known as Splinterwing, is a two headed abomination mutated by the raw powers of Chaos, and is the steed of Egrimm van Horstmann, traitor of the College of Light and favoured of Tzeentch. This massive monstrosity is bloated and warped beyond recognition; with folds of black-grey scaled flesh bulging over the tops of its legs, a crooked back ridged with plates of bone, and a thick tail more akin to a deadly spiky club. One head is bestial; with a brutal under-shot jaw full of upwards-jutting fangs, with tiny red eyes buried in ridges of bone. The other head is clever; its frame long and slender, a greenish tongue that lashes like a caged snake, and with eyes that are sharp as steel. With one head spouting out black fire, and the other spewing out acidic bile, Baudros is destruction incarnate, leaving naught but ruin in its wake.

During the time of Magnus the Pious, Baudros was awoken from his slumber by the foul winds blowing south during the Great War Against Chaos. He was a threat to all of the Empire, bringing devastation and spreading the foul taint of Chaos. It was only by the efforts of Teclis, High Loremaster of Hoeth, one of the most powerful sorcerers the world has ever known, to defeat him, but not even Teclis could finish off the beast. With no other option, Teclis imprisoned him in a magical prison buried in the ground, which eventually became the location of the College of Light, which sits right on top of this hidden prison. The greatest defense against the release of Baurdos was that no mortal knew about its whereabouts... No mortal exepct Egrimm van Horstmann.

Tzeentch, the God of Magic, whispered to van Horstmann the location of Baudros' prison, and the corrupted sorcerer summarily released the warped dragon. Van Horstmann made a pact with Baudros, and he escaped the College of Light, blasting through the College with tainted fire, and flying north towards the Chaos Wastes, of course right before a brief detour...

Source

 * Realm of Sorcery (2nd Edition Fantasy Roleplay)
 * pg. 88 - 89
 * Van Horstmann(Novel) by Ben Counter
 * Prologue
 * Chapter Seventeen