Pirate Captain

The title of Captain can refer to either a Captain of a pirate crew, or a rank in the Marines (note however, that this is meanly a coincidence in the English translation, as japanese words for the two are not the same).

Pirate Captains

 * Monkey D. Luffy
 * Red-Haired Shanks
 * Buggy the Clown
 * Kuro
 * Don Krieg
 * Arlong
 * Whitebeard
 * Blackbeard
 * Bellamy
 * Montblanc Cricket
 * Foxy the Silver Fox

Former Pirate Captains

 * Alvida
 * Jango (was Captain of the Black Cat Pirates in Kuro's absence.)
 * Wapol

Marine Captains
A marine captain (taisa) is a rank junior to that of a Commodore. It is second most seen rank in One Piece to date, having 8 representatives and being second only to that of Vice Admiral in terms of appearance. The number of seen captains MAY have surpassed the number of seen vice admirals, during the Enies Lobby assault on the Bridge of Hesitation, where no one bellow the rank of captain was to attack, we have not seen many of them more then once and from afar, except three (Sharingu, Shuu, Very Good) however, these were never specifically reffered to as "captains", until being dubbed as such by Oda in the SBS of volume 47.

Trivia
Any naval officer below the rank of captain who commands a ship, is addressed as "captain" while aboard that ship, by naval custom. The ship's captain also may be referred to as the Skipper. A naval officer with the rank of captain traveling aboard a vessel he does not command is either never referred to by rank, or in some navies, is addressed as Commodore to avoid confusion with the ship's actual commander.

Curent

 * Hina
 * Nezumi
 * T-Bone
 * Very Good
 * Sharingu
 * Shuu

Former

 * Smoker-promoted to Commodore
 * Morgan-excluded from the Navy