2 – Monkey D. Dragon commonly known simply as ‘Dragon the Revolutionary’, is the father of the Monkey D. Luffy and the son of the Marines hero Monkey D. Garp. Dragon is the infamous founder and leader of the Revolutionary Army who has been attempting to overthrow the World Government. Dragon is the World Government’s greatest enemy, and is the most dangerous and most wanted man in the world. I think Monkey D. dragon is the most powerful one among the others I have mentioned in my list and also he can defeat a Four Emperor’s/Yonko .
3 – Monkey D. Garp He is a legend among the marines and grandfather of Monkey D. Luffy . I don’t think anyone needs any explanation why Monkey D. Garp is in this list . If you have Read the Manga or watched the Anime, then you already know that his caliber far surpasses others . At his Younger age , Monkey D. Garp was the only Marine who was able to fight the King of the Pirates , Gold D. Rogers . There are many back story talks ,everyone mentioning that there were many times when Garp almost killed Gold D. Rogers . Also During the War of the Best , when Sakazuki killed Ace , Monkey D. Garp’s adopted grandchild he couldn’t control his anger . He was going to kill Sakazuki , but Sengoku stops him . If you remember Monkey D. Garp’s Dialogue , It was “You’d better not let go of me , Sengoku.. Otherwise I will kill that Damn Sakazuki (Akainu) . Well that was a very bold Dialogue and I think if Sengoku hadn’t stopped Garp. Monkey D. Garp can also use all the three types of haki , also during the battle at marineford when Monkey D. Luffy Used Conqueror’s Haki Monkey D. Garp wasn’t Surprised , he said that it not a surprise he has Inherited That Power.(Which further signifies that Monkey D. Garp can use conqueror’s haki) . There are tons of other facts that proves that he can beat a Four Emperor’s , but I think this much is enough to convince you all about what I am trying to say .