I think it's pretty much in the evidence that he was a solder of the West (From the Provence or the Free Citys) and not a Berzerk or Fir'bolg.
Think of it. He had fought through pretty much the whole war, as is attested to in some of the last missions ("I am not a coward... my actions over the last 17 years prove this...) So that excludes the Fir'bolg, as they did not come in right away.
Also, the Northmen probably did not get as involved in the fighting West of the mountans untill after Covenent fell. Why? Because they had to make sure the dark did not come and destroy their own home's after the Cath'bruig Empire failed.
Therefor, he is most likely a solder from the Provence. More specificly, I think he was probably from Covenent, as the mission to that city was called "Homecomeing".
That's all... hey that's the first story related post I've made in a long, long while;)
See you folks around.