Admiral

Admiral (大将, taishō) is a title of admiral signified senior command rank in the Marines. Admirals, also known generally as flag officers, were typically responsible for a high level military command at battle group or fleet level, and/or for administrative and political duties relating to Marine operations.

In One Piece, Admirals are shown as being the second highest rank behind the Fleet Admiral.

Marine Admiral
In the One Piece world, there are only three Marines with the title of Admiral. They are known by their aliases, "Aokiji" (Blue Pheasant), "Akainu" (Red Dog), and "Kizaru" (Yellow Monkey). The Admirals and Fleet Admiral Sengoku are the only Marines within the World Government who have the authority and ability to issue a Buster Call.

The Admirals are crowned the World Government's "Ultimate Attack Force", and are the strongest individual fighters within the World Government and the Marines.

One former Admiral has been shown since One Piece began and that is Fleet Admiral Sengoku; this was seen during Episode 277.

Should a World Noble be opposed, or injured, an Admiral will be summoned to take down the assailants who did the damage.

Trivia

 * The two Admirals introduced so far (Kizaru and Aokiji) are both based upon Japanese actors and are drawn to resemble them. Both Admirals also have Logia class Devil Fruits (somehow related to the color in their aliases, blue for ice and yellow for light).
 * Their aliases are taken from Momotaro legends, there are a pheasant, a dog and a monkey assisted the boy hero, Momotaro on his adventures.