Monkey D. Dragon

Monkey D. Dragon is the father of Portgas D. Ace and Monkey D. Luffy and the son of Monkey D. Garp. He is the infamous Revolutionary Leader and has been causing trouble around the world.

Appearance
He is often seen in a long green cloak and recently he wears the clothes of a revolutionary. He has, what resembles, tribal tattoos on the left side of his face and spikey black hair with a widow's peak hairstyle. He is almost always seen with a smile on his face.

Personality
His personality is mostly unknown due to the many mysteries surrounding him, save for an apparent love for freedom and belief in fate, which are traits of a D. Unlike other members of his family, or D's for that matter, he looks stern and serious, though in all his appearances so far, he wears a smug grin. He speaks as though he is a mystic of sorts.

Monkey D. Garp
Dragon is the son of Garp. No direct interaction has been seen between the two, however, Garp was casual towards telling Luffy about Dragon's role. He even laughed when he realized he shouldn't be telling people this kind of information. It does seems to be there is some sort of interaction between the two, as Garp stated, that the reason why Dragon was in Logue Town, was to see Luffy off.

Portgas
Ace's mother thus far has only been revealed by the name of Portgas. It is unknown what the relationship between her and Dragon is like. It is likely that she is also Luffy's mother as well. The controversy over the name discrepancy between Luffy and Ace (as to they're relation) was resolved when Ace's true name was revealed to be indeed Monkey D. Ace, but that he had changed it by taking up his mother, whom he had memories, respect, and almost without a doubt, love for. While his father he had no memories of. Rather than stating abandonment, or something similar, Ace chooses the term memories, insinuating that Dragon was around, at least for a little while but never made an impression upon him as a child.

Portgas D. Ace
Most recently has it been revealed by Ace that he took the name Portgas after his mother, claiming that his relation to Dragon is only through the blood he has running in his veins. Ace is shown with a disdain for his father, noting that he recognizes Whitebeard as his father.

Monkey D. Luffy
Luffy is Dragon's son. Like his father Garp, he seems to hold high expectations for Luffy and although has not introduced himself to him, seems to support his son's actions so far.

Other
No mother has been named for Dragon, however both were left as "?" in the supplement issue The Grand Line Times. As a carrier of the Will of D he may also be related to other D's.

Abilities and Powers
Little has been revealed about Monkey D. Dragon's abilities; however, he is the leader of the Revolutionaries and has full command of the organization.

Past Story
Dragon's history remains mostly a mystery, thus it is unclear why Luffy was left to be brought up by his grandfather Garp instead of himself. At some point he began the Revolutionary movement becoming its leader and his ideals began to slowly spread throughout the world. One by one countries slowly began to support him, though sometimes through war.

The little known history on him is that six years ago, in the Council of the Kings in Mariejois, the purpose was to discuss his revolutionary movement and his ideals that were threatening the World Government. Thalassa Lucas showed the picture of him. It was then he revealed that Dragon was currently no real threat, but would become so, in 5-6 years or so, if not dealt with.

Logue Town Arc
His first appearance was during the Loguetown Arc where he saved his son Monkey D. Luffy from Captain Smoker. At that moment a gust of wind passed through Loguetown blowing Luffy, Smoker and Buggy the Clown away. It's not known if he controlled the wind that blows off the marines at this point, but in the manga he did say the word "Storm" as the wind passed by and seemed untouched by it.

Post Enies Lobby Arc
While visiting Luffy, Garp let slip that Dragon was Luffy's father in a causal conversation with him. The reaction of those present was of dire shock. It was then revealed to Luffy just who his father was by Robin.

Robin stated that he was the top of the revolutionary army and has spread his ideals to every nation and kingdom, causing many of them to fall into his hands. He manages to stir rebellion around the world and has successfully pushed the world towards civil war. His actions greatly anger the World Government and he is considered the most dangerous man in the world. Until that moment, no one had known anything about Dragon, not even his full name.

Current Events
He has since reappeared again on Paladego. Seeing Luffy's new bounty one of his men was about to tell him that Luffy was Vice Admiral Garp's grandson when Dragon stops him and says he will stay in the wind for a while. He walks out into the castle's balcony where he remarked that the true nature of the world will be answered and he will meet Luffy again.

Trivia

 * Dragon has been the center of several myths among fans.
 * Whether it is a foreshadowing on Oda's part or a coincidence, Luffy appeared in the short Mugiwara Theatre - Monster Time as a dragon years before he was revealed to be Dragon's son.