Story behind him and any other guard that end up in my everso small traitor guard is that they were from a former penitents regiment that somehow managed to defect and after battles, etc found that allying themselves to Chaos was the best way to secure their survival. (Little did they realise the bargain they had gotten into....) Chaos Undivided though and not Nurgle like my Plague Marines. Thought it'd make me have to think up of a more interesting story of why they would fight/work together in the 1st place. :)
(Again, he's a tank commander so has no legs.... Just in case you were wondering about why he's stuck to the top of a cork.)
And a brighter pic of the front view which shows more detail, but washes out the hard earned shades.