One Piece is so empowered by the 'found family' trope that biological family members don't come up very often if they're not already "just the worst." In fact, it wasn't until the end of the Water 7 and Enies Lobby Saga that readers finally learned a bit about Luffy's family through his grandfather, Monkey D. Garp. Here's everything we know about Luffy's grandfather -- and how he's both similar and different to Luffy.
In typical Eiichiro Oda fashion, Garp was referenced and introduced in One Piece far before his true reveal -- fans just didn't know it at the time. Luffy's grandfather first appeared in the side story Koby and Helmeppo's Chronicle of Toil, which explores the two young men's lives after separating from Luffy and Zoro and joining the marines. Garp arrives to oversee the transfer of former marine captain Axe-Hand Morgan, but is unwittingly struck down by Morgan as the criminal takes his own son hostage as a method of escape. However, Morgan didn't actually get the jump on Garp. The easy-going marine vice admiral just fell asleep while standing up, as you'd expect. In the end, he takes both Koby and Helmeppo under his wing and they transfer to Navy Headquarters to begin their training under his guidance.
The first time One Piece fans learn Luffy has a grandfather is from Admiral Aokiji in Chapter #319. Aokiji says Luffy is just like his grandfather -- wild and has no control -- and then mentions that he owes a great debt to the man. However, Garp isn't fully unveiled until Post-Enies Lobby where he visits Luffy and his Nakama, and also tells them about Luffy's father, Dragon.
Garp is not only a Marine Vice-Admiral, but has been called the "Hero of the Marines" for his decades of service. At one point he fought alongside Gol D. Roger to stop Rocks D. Xebecs and his crew, consisting of Big Mom, Kaido and even Whitebeard at God Valley. Much remains unknown about the God Valley Incident, but we do know it's what earned Garp his title.
Furthermore, Luffy's grandfather has been offered the promotion of Admiral on numerous occasions, but has refused it every time. This is because Admirals can be called in service of the Celestial Dragons, something Garp wants nothing to do with. It seems dislike of the Celestial Dragons is indeed a shared trait by those of the Monkey family in One Piece.
Despite his differing adventures, Garp does have a lot in common with Luffy. The old man is as blunt and stubborn as his grandson and also suffers from narcolepsy and an enormous appetite -- though Garp seems to have a preference for rice crackers over meat.
As a parent and guardian, Garp is a danger at worst and negligent at best. In service of making Luffy stronger, Garp tossed him into a ravine, left him in a jungle, and tied him to balloons. Then he left Luffy in the care of the Mountain Bandit Dadan alongside Ace. Still, Garp would occasionally check up on the two boys from time to time, and wanted to see them become respectable navy men. With his grandsons as pirates, Garp is left feeling proud of their outrageous accomplishments, even at the expense of the marines' credibility and standing.
What makes Luffy's grandfather interesting, though, is how duty as a Marine gets in the way of his love for his family. During Ace's execution, Garp could neither bring himself to help the marines, nor save his grandson. Instead, he elected to sit down and stay beside Ace until the very end, not wanting his grandson to be alone should he die. In fact, after Akainu killed Ace, Garp had to be restrained from killing the inhuman admiral. Monkey D. Garp is unquestionably one of the best Marine characters, and likely still has a deeper role to play once One Piece reveals more about the God Valley Incident and his past.
