Antagonist
Character Role Analysis
King Philip/Louis the Dauphin
We're splitting the antagonist role into two for the same reason that we split the protagonist role into two: it reflects the shift that occurs between the two halves of the play. In the first half of the play (Act I-Act III), King Philip is the main antagonist, the one who brings an army to face down King John over control of Angers and other territories (including England itself).
Even a marriage alliance isn't strong enough to keep these two monarchs from getting back at each other's throats when Cardinal Pandolf comes knocking. And yet, in the second half of the play, King Philip is entirely absent, having delegated all authority to his son, Louis the Dauphin.
Thus, you could say that the first half of the play features two members of the older generation fighting it out, while the second half of the play shows the mantle being passed to the younger generation.