Oda likes to use myths, legends and fables, e.g. “Fable” backwards = Elbaf. In chinese mythology, there are said to be 4 seas: North, South, East and West.
Those 4 seas are represented by four colors: Yellow, Blue, White and Red. They have also been represented by different animals over the time including a Monkey, a Bird, a Dragon, and a Dog. This of course screams:
A north sea with a yellow monkey = Admiral Kizaru
A south sea with a blue bird = Admiral Aokiji
A west sea with a red dog = Admiral Akainu
-> That would leave the East Sea = Admiral White Dragon (Shiroryu)
There is a similar myth that supports this: The myth is about a king who had 4 loyal followers: One had the shape of a bird, the 2nd the shape of a monkey, the 3rd the shape of a dog, and the last the shape of a pheasant. Some day, the bird realized how evil the king was, so he left his king, but not without letting the other followers know the truth. To his disappointment, the dog was too loyal to his king, the monkey was an idiot and he couldn’t understand what’s going on, and the pheasant was simply too lazy to do something. Now all this resembles the Admirals in One Piece a lot. The colours + the animals + the attitudes! (This time, the bird = dragon)
I believe that Akainu’s loyalty to the Navy and the Absolute Justice, Kizaru’s (pretended) goofiness, and Aokiji’s laziness are taken from those myths, hence I believe that the White Dragon, who saw the truth about the evil of his king, is Monkey D. Dragon, Admiral Monkey D. Dragon, with the person of the “King” being taken by the institution of World Government.
Growing up as the son of the famous and renowned Marine officer Monkey D. Garp, combined with the experiences of racism, humiliation and discrimination he made while living on Dawn Island, it’s plausible that Dragon joined the Marine or the World Government with hopes of changing the world. But he had to realize (like the Dragon in the myth), that the World Government is too evil, too set in their ways, and that the system couldn’t be changed. He deserted his position, formed the Revolutionaries and dedicated 100% of his effort to achieving his goal: Changing the world, changing the system, erasing racism, discrimination and humiliation from the world.
I say “dedicate 100%”, because he didn’t even take care of his own son, or he wasn’t able to take care of him. Whatever the case may be, something must have happened in his life, to trigger a young man to abandon his former life and to start a life of secrecy and rebellion. And since love & romance are not a big subject in One Piece at all, I doubt that his Wife (Luffy’s Mom) or even Garp’s Wife (Dragon’s own Mom) have much to do with this. I believe the evil of the World Government, that he experienced at first hand, triggered Dragon’s decision to start a Revolution.
*Theory by Gobee129