Strength/Int based knife-fighter:
Barbarian 7, Swashbuckler 3, Rogue 3, Fighter 2, Invisible Blade 5.
May need some tweaking, but it's a decent start.
Swashbuckler and Invisible Blade give you Int Synergy for AC and Damage.
Rogue adds more sneak attack/stealthiness.
Barbarian adds the brutality that Riddick displays and higher HP
Keep Int and Strength high - Dex may only need to be middle of the road. Remember, just because you use CAN use Dex bonus for finesse weapons doesn't mean you HAVE to, so just use your strength bonus to hit with if you want to stay focused on strength.
Take some grappling and trip feats (Riddick uses grapples and throws heavily in his fighting style). Daggers and Kukris can be used in grapples, so grappling someone and then stabbing them to death could be a very effective (and cool) tactic.
You could even nix invisible blade from the build completely if you wanted to (pre-req feats are throwing based, which the Riddick does little of). Add in some other 5 level PrC, like that fear/sneak attack based one from Complete Scoundrel (can't remember what it's called...)