Sakazuki, commonly known by his alias Akainu, is the current fleet admiral of the Marines, succeeding the previous fleet admiral, Sengoku. During the first half of the series, he was one of the three admirals, and the last one to be fully revealed. He ascended to the position of fleet admiral after defeating Kuzan in a ten-day duel that left Punk Hazard in its current state. One of his first decisions was to relocate the Marine Headquarters into the New World in preparation for the New Pirate Age.
In the manga, he was first mentioned by Nico Robin during the initial encounter with Aokiji. In the anime, he was mentioned earlier by Vice Admiral Jonathan during the anime-only G-8 Arc, which aired after Akainu had been revealed in the manga. 
Because of his actions, Akainu was one of the main antagonists of the Marineford Arc and after his promotion, he became one of the main antagonists of the series.
Sakazuki is a strident follower of Absolute Justice, to the point where his extremism prompted an equally high-ranking colleague to resign from the Marines. He believes that a person’s heritage is a reflection of how big of a threat they pose – a belief which caused him to target Portgas D. Ace and Monkey D. Luffy during the Battle of Marineford for the purpose of purging their “bad blood”, which ultimately led him to personally kill Ace and attempt to kill Luffy, which he failed to do – managing only to leave a massive scar on his chest.
Sakazuki is an incredibly tall, light-skinned, unusually muscular man (the most muscular of the former admirals). He’s about as tall as his fellow admirals, with a square-shaped face, very pronounced facial features and short black hair. He usually wears a standard Marine cap and sports a crimson, double-breasted suit, decorated with what appears to be a pink rose on his left buttonhole. Unlike many high-ranking Marines, he does not wear a tie, but instead leaves his light colored flower-patterned shirt unbuttoned showing his muscular neck and part of his tattoo. He wears black gloves and shoes. Although not canon, the anime shows his height was somewhat taller than the 301 cm tall (9’8″) Jinbe.
The tattoo on the left side of his chest is black (light-blue in the anime), containing numerous images of flowers integrated into its design. Sakazuki’s tattoo has flame-shaped edges and it extends from the admiral’s left shoulder to his hip, covering part of his back and ribs. He has another, smaller tattoo in the shape of a black sword on his right deltoids and a small part of the biceps. In the anime, his eye color is seen to be brown and this was also shown in a colored drawing by Eiichiro Oda.
In his youth, Sakazuki wore an open red shirt and carried a Katana on his back, as well as a set of khaki pants held up with a loosely tied yellow-orange ribbed belt with a siver bullseye-shape buckle, and pair of red sneakers. 
Twenty-two years ago, at the Ohara Incident, he wore a simple white Marine cap under a dark gray hood that seemed to be a part of a cloak he wore beneath his suit, or Marine coat. Until getting off his chair in order to destroy an incoming iceberg during the Battle of Marineford, his face was always hidden by the bill of his cap.
As a child, Sakazuki still had the grim disposition he retained as an adult. He also wore tattered clothes and carried a dagger. He wore a cap similar to the Marines’ cap he would don in the future, except it has the kanji for “justice” instead.
After the time-skip, as a result of his intense battle with Kuzan at Punk Hazard, the right side of Sakazuki’s neck and face are scarred, and a chunk of his right ear is missing. In addition to his injuries, he also grew a mustache and goatee. He has also replaced his trademark red suit for a white one, similar to what Sengoku wore when he was Fleet Admiral; however, Sakazuki still wears the same floral pattern shirt underneath and doesn’t wear his black signature gloves. He is also frequently seen smoking a cigar.
|— Sakazuki’s view on destroying the ship of survivors during the Buster Call at Ohara|