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 most powerful rank behind the Fleet Admiral.

Marine Admiral
There are only three Marines with the title of Admiral in the Marines. They are known by their aliases, "Blue Pheasant" (Aokiji), "Red Dog" (Akainu), and "Yellow Monkey" (Kizaru). These are similar to characters in the fairy tale Momotaro. These three admirals and the Fleet Admiral are the only Marines within the World Government who are capable of issuing Buster Calls.

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

Should a World Noble be opposed, or injured, one of the three Admirals 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.