
Summary
- Monkey D Garp and Gol D Roger were shown as strongest marine and pirate
- Garp and Roger trust each other a lot even after being enemies
- Roger and Garp could actually be siblings and that would be revealed in the final saga
In One Piece, the author Eichiro Oda left a lot of loopholes in the series which always urges the fans to develop their own theories and hints. One of the major theories that seem relevant to the storyline also seems acceptable is the one that Monkey D Garp, the Hero of the Navy, and Gol D Roger, the King of the Pirates are brothers.
Bond Between a Pirate and a Marine
Even though having popular names in their field as a Marine soldier and the Pirate King they both seems to share a very good bond between each other. Garp always have great hatred for pirates and never wants to look mercy for them but for his fight against the Rocks Pirates, Garp took the help of Gol D Roger to defeat Kaido, Big Mom, Whitebeard, and Xebec D Rocks on the Pirate Island, Beehive. This is an odd move from Garp to accept a help from a pirate to fight alongside.

Entrusting Ace before his Death
When Roger decided to surrender himself up to the Marines he entrusted his unborn child to Garp to take care of the child and protect the child from the fact that it is Roger’s child. Even after being enemies, Roger believed that Garp could save and look after his unborn child other than his pirate crew nakamas. Roger tells the place where Portgas D Rouge is hiding. Also in the flashback episode, Roger tells that Garp and Rouge are related to each other, but the exact relation between each other was not revealed only visible similarity was the surname “D” in their names.


Sharing the Will of D
The most important thing that both Garp and Roger have the Initial D in their names which implies that they both are the Will of D. Both the perspective family of Garp, Roger, Luffy, and Ace possess the Conqueror’s Haki within them except for Dragon whose power isn’t revealed yet however he is also sure to have it.

Garp’s hate for becoming Pirates
Garp never wanted both Luffy and Ace to become a pirates in the future and he always insisted them to become marines. This is maybe because of the fact that he couldn’t save his brother Garp from the execution. Most notable is that Garp was never present in the Garp’s execution in Loguetown.



Possibilities of Being Twins
In the beginning of One Piece, it was said that it was said that Garp was 75 years old and Roger was said to be executed before 22 years, where he was 53 year old. This claims they both were of same age which strengthens the theory more. The theories of Roger and Garp being twins but not identical ones are stronger. Garp, Dragon, Roger, Luffy, and Ace they all share a similar face appearance and exact smile replica of each other. However, they both carry differing first names which may have to hide the fact that they both are related to each other.

Even though the author has finished the death story of Roger and Ace, more stories related to them will always be present in the upcoming panels. In the Egghead Arc, when King Cobra tells Sabo about the secret of Will of D, Sabo remembers his childhood days with Ace and Luffy where he himself was confused about the similarities they had.