Garp was the one who chased after Roger and tried to stop him. After Roger surrendered himself, because he was ill, Garp visited him in the prison.
Who would have taught that Roger would ask Garp to take care of his child. They were enemies, but they were human before everything.
Garp had a dream that Luffy and Ac will follow into his footsteps and become marines. Instead Shanks influences Luffy and Luffy decided to become the next pirate king.
Ace followed his dream too and ended up being in Whitebeard’s crew. Garp must be doing some photoshop now and making them look like marines.
When he was a child and a very young Marine, Garp greatly resembled Luffy, although he was apparently more muscular than his grandson. As a child, he wore a tropical-like button shirt with shorts. He is seen wielding a pipe staff and carrying a treasure chest while riding a tiger he tamed. It is unknown when Garp got his scar on his left eye, but he already had it in his childhood days.
In his free time, such as when visiting Ace or Luffy on holiday, Garp favors wearing sandals, one out of an assortment of tropical shirts and light-colored shorts. He was also seen with said shirts, black trousers and boots.
Garp displays an intelligence level that is equivalent to that of Luffy’s; however, Garp seems somewhat more absent-minded and sadistic than his grandson. Due to his hot temper, he is unable to accept excuses (and is exceptionally poor at creating his own) and at times likes to enforce his point of view on things simply through force, namely hitting them across the skull (When used on his grandsons, he dubs this “Fist of Love”.). Garp also has his own laughter style: he adds either Bwa or Wa before the haha part.
He, like his grandson, has an extreme fondness for food; in his case donuts and rice crackers. Also, like both of his grandsons, he seems to fall asleep at random times as seen in Water 7 when he was punishing Luffy for the skirmish he caused.
After arriving at Water 7, he went to the small house where Luffy was recuperating from his battles at Enies Lobby. Vice Admiral Garp marched to the front of the temporary Galley-La headquarters, and tells two subordinates in specific to wait outside. Garp breaks through the wall and into the Straw Hats’ room.
Everyone prepares to fight, but before they can do anything, Garp bypasses them and punches Luffy’s head into the floor, telling him to wake up. To everyone’s surprise, Luffy screams in pain. Garp then says that no one can escape his Fist of Love. He then removes his mask and tells Luffy he heard he had been doing reckless things. Luffy is shocked to see that the man behind the mask is none other than his grandfather, and everyone else is even more surprised that Luffy’s grandfather is a high ranking Marine. Garp tells Luffy he owes him an apology.
As the “Hero of the Marines”, Garp is overall very well-respected for cornering the Pirate King multiple times. While Garp seems devoted to his duties, he has his own sense of justice and does not always obey orders given to him.
Aokiji, in particular, has been indebted to Garp due to a certain incident that involved Garp saving his life, and is impressed that Garp refused several promotions, while Akainu has earned the vice admiral’s hatred for killing Ace. He was requested to remain behind as an instructor due to his fame, which will be influential in recruiting.
It was revealed that during the Reverie at Mariejois, capital of the World Government, six years prior to the beginning of the story, Thalassa Lucas brought up the problem that Dragon, leader of the Revolutionaries, was getting stronger and that in five or six years he would be a menace to the World Government.
At some point before the Enies Lobby incident, three CP9 assassins, Jabra, Fukuro, and Kumadori, were sent to an unnamed town to assassinate three important revolutionary leaders (Dragon not included). However, they are also forced to eliminate twenty extra people thanks to Fukuro revealing his unit’s presence and their intentions to the town.