An antagonist must be equal to or more powerful than the protagonist. He ought to be smarter, stronger, more sophisticated, more cunning, more driven, richer, suaver, more handsome, etc. It ought to be obvious that the protagonist is less than likely to succeed in overcoming whatever it is that the antagonist puts in his way. Such is the power an antagonist has over the protagonist. The paths of these two must either cross or intertwine a lot. In all cases the antagonist ought to be a source of deep frustration for the protagonist.
