Monkey D. Garp

Monkey D. Garp is a Marine vice admiral. He is the father of Monkey D. Dragon, the grandfather of Monkey D. Luffy, and the adoptive grandfather of Portgas D. Ace. He took charge of both Coby and Helmeppo's training. After the war, he became a Marine Instructor to train new recruits.
Garp is one of the major figures, along with Sengoku, Shiki, and Whitebeard, from the times when the "Pirate King" was still alive.