Cristobal Maxia is an elite army veteran and heavy weapons designer who leads a post-game FND insurgency in Balaceras. He hides behind deployable ballistic shields, so plan how you will get around them.
Cristobal went back to the army to lead FND holdouts after Castillo's fall. If he is family to Meagan, his relatives also include a famous FND bodybuilder and a Libertad guerrilla.
Do not trade fire with him head on behind his shields. Flank, use explosives or blast ammo to clear the cover, and stay off his line of fire while you reposition.