Fortitude
Combat
In combat Fortitude negates 1 damage per level per combat round. Furthermore you can ignore aggravated damage for as many rounds as you have Fortitude, taking it as normal damage (reduced by Fortitude as usual).
Utility
Fortitude allows you to resist even mental assault, when defending against any power that compares against your Mental Ability treat it as 2 higher for every level in Fortitude.