Whitebeard. Made arguably the best arc of the series what it was. Basically set the standard for strength, fame and accomplishing one's goals aside from Roger and we actually got to see what that entailed first hand. He's just an incredibly character, very cool, very formidable, placed family above wealth and other material desires and had the greatest death in the series and one of the best I've seen in a manga. Just a tremendous, larger than life character.