Sakazuki

Admiral Akainu (赤犬大将, Akainu Taishō), formerly known as Vice Admiral Sakazuki (サカズキ中将, Sakazuki Chūjō), is an Admiral of the Marines, one of only three to hold such a position and subordinate only to Fleet Admiral Sengoku. "Akainu" translated to English means "Red Dog".

Appearance
Twenty years ago at the Ohara incident, he wore a simple white marine cap and he also wore a dark gray hood that seemed to be a part of a cloak he wore beneath his suit, or marine coat. Like any other high ranking marine, he was dressed in a simple white/gray suit with a white marine coat draped over his shoulders. His entire face was not seen during his appearance, as it was hidden by his cap.

At the execution of Portgas D. Ace; Akainu is seen wearing a dark-colored suit, with a flower greatly resembling a rose on the left side of his jacket; underneath this he wears a shirt with floral print. He is also wearing black gloves and boots and the same Marine cap covering the top half of his face.

Akainu has a square-shaped face with hollowed out cheeks. There also appears to be a tattoo on the left side of his chest, but it is largely obscured from view by his shirt. However, from what is seen, it appears to contain numerous images of flowers integrated into the design. He appears to be just as tall as his fellow Admirals, Aokiji and Kizaru.

Personality
We have to be thorough! If even one of those scholars made it onto that ship, all of the sacrifices we've made would be for nothing! We must eliminate the very possibility of this "evil" existing!!

— Akainu's view on destroying the ship.

Akainu is a firm believer in "Absolute Justice", ruthless to the edge in maintaining justice. Of the three Admirals, he is the only one who has maintained a dead-serious disposition in all of his appearances.

Akainu's beliefs led him to go as far as destroying the refugee ship simply due to the possibility of even one scholar sneaking on board. His logic is that if even one of the scholars of Ohara had escaped with it, the mission would've been a failure, much to the dismay of Aokiji, who called him a fool for overdoing things.

Additionally, he seems to have little tolerance for Marines who desert their post, even though that soldier did so for the sake of his beloved family. What exactly he does to them, however, remains unclear, but it seems that he kills them using his lava-based unnamed Devil Fruit powers.

He is one of the few who knows that Luffy is Dragon's son. Whether he has some relationship with Dragon or if some of the Marines know that Dragon is Garp's son is unknown.

Abilities and Powers
As an Admiral, Akainu is able to command vast number of Marine troops that are under his rank. Most of all, he has the ability to order a Buster Call attack on any island. In addition to this, given that he holds the same rank as Kizaru and Aokiji, it can be assumed that he commands comparable fighting abilities to those two. In the manga, it appears that Akainu and his fellow Admirals have very acute hearing. They were able to hear activity underwater before anyone else.

Devil Fruit
Akainu possesses an unknown Devil Fruit that gives him control over volcanic rock and lava.
 * Great Eruption (大噴火, Dai Funka): Akainu creates a fist made out of pure molten rock. He can also create volcanic rocks and strike them similar to meteors. This was first seen when he used it to evaporate an iceberg hurled at his fellow Marines by Jozu. According to spectators, the battlefield after this one attack resembles the apocalypse.

Ohara Incident
He was known as Vice Admiral Sakazuki before his promotion. He was present at the Ohara incident, being one of the five vice-admirals, leading the Buster Call offensive. He ordered the destruction of an evacuation ship of civilians and soldiers, claiming it needed to be destroyed in case a single scholar managed to sneak on board (an action that horrified even Spandine).

Current Events
Vice Admiral Momonga mentioned to Boa Hancock that the three Marine Admirals, including Akainu, will lead the Marines against the Whitebeard Pirates following the announcement of Portgas D. Ace's execution. Akainu was seen sitting beneath the execution platform of Portgas D. Ace with his fellow Marine Admirals.

Akainu stepped into the battle when Jozu hurled a massive iceberg, displaying abilities to control volcanic rock by launching a fist made of lava to destroy the iceberg and sending small burning rocks flying all over the place, destroying one of Whitebeard's ships.

He is later seen confronting a Marine officer who is fleeing from the battle not wanting to die out of concern for his family. Akainu attacks, and apparently kills, the Marine officer for this "cowardice", much to the horror of Coby and Helmeppo who were watching (having nearly ran into the Admiral themselves doing the same action). Akainu then receives a report on the Den Den Mushi that the preparations for Sengoku plan are set.

Luffy's arrival at Marineford has Admiral Akainu commenting that, as the son of Dragon, Luffy is one pirate who must be eliminated at all costs.

Trivia

 * The way Akainu's character design is drawn resembles the famous Japanese actor, Bunta Sugawara. Akainu's real name, Sakazuki is apparently based on the three movies of Bunta Sugawara with "Sakazuki" in the title.
 * His name and other Admiral names (Aokiji, Akainu, and Kizaru), are taken from Momotaro legends (Momotaro met Pheasant, Dog, and Monkey as friends to accompany him in his journey)
 * Before being revealed in chapter 554, Akainu's abilities were the center of many myths among fans.