Main Antagonist In One Piece : There's not really any main villians one piece, there are people that luffy will bound to run into later in the series like black beard and the three admirals but they will not be the main antagonists until they appear in their arc, each arc in one piece has it's own main antagonist because luffy's goal is not.
Main Antagonist In One Piece - Final villains traditionally tend to show up quite late in moreover, finding one piece and becoming the pirate king is shown as the main goal, but is in reality not.