The God of War himself fits perfectly into the brutal fighting franchise, as clearly shown by the below gameplay video.
Seriously now, that's absolutely awesome and a great bonus for PlayStation 3 owners. There's also a great video on the PlayStation Blog where Ed Boon and Stig Asmussen (director for God of War III) discuss the marriage of the two franchises, and you can check that out below.
For fun, I tried thinking of an Xbox 360 exclusive character that could work well for that platform's version of the game, and I honestly came up short. Not because the Xbox 360 lacks quality exclusives or characters, but because they're exclusive franchises are primarily sci-fi or shooters and they simply wouldn't mesh as well.