Portgas D. Ace is an extremely important character in One Piece who played a significant role before the time skip. Being Luffy's older brother, Ace was absolutely essential for the plot to move forward. He drove one of the biggest and the most popular segments of the entire story, the Summit War Saga, as much of that revolved around a war to rescue him from the clutches of the Marines, and at the same time, giving Luffy a reality check and forcing him to grow stronger.