[@Balthazar007]
I was thinking of a few things. 

Bountyhunter/Assassin - Someone who captures or eliminates specific targets for a price. 
Lord of War - Someone who sells weapons/information to both sides. 
A scientist trying to unlock the next evolution or mutation for their species if not mix both. Ohh such a taboo. 

I was thinking that in any case, the body he jumps into is trying to find a way to stop the war. He could possibly have started another faction or is part of one. Mainly I would like to know a lotta bit more about the people at war and how they govern one another. Like is there an agreement in using or not using specific types of weapons? How do they eat? Are there rules in not harming Civilians? Does this world have special animals and wildlife? I mean I wouldn't mind having him be a Gladiator or someone in the military it just depends.