Queen (Title)

A Queen is a female monarchic ruler of a kingdom.

Queens in One Piece
Under normal circumstances, diarchic kingdoms are ruled under both the king and queen, alongside each other as husband and wife. However, at least in Amazon Lily, only women are allowed to live there, and as such, the queen (or empress) is the absolute monarchy of the kingdom, with no king or prince of any kind.

As with kings, the quality of a queen's rule is dependent on her personality, whether benevolent or corrupt. Nefertari Titi, Gloriosa and Otohime all seemed to have great care of their respective kingdoms, with the latter even taking trivial matter into her own hands that is unfitting of a queen. On the other hand, a cruel woman may be rather tyrannical to her people, as seen with Boa Hancock, who was jaded by her past and acted cynical to everyone, and using her physical charms to justify her actions, which, nevertheless, prevented her people from getting angry with her (so long as they do not know of her said past). Miss Universe married her king husband after he created his new found wealth and power,

Current Queens

 * Boa Hancock is the empress of Amazon Lily.
 * Miss Universe is the queen of the Black Drum Kingdom.

Former Queens

 * Nefertari Titi is the late queen of Alabasta.
 * Gloriosa is the former empress of Amazon Lily.
 * Otohime is the late queen of Ryugu Kingdom.

Translation and Dub Issues
While "queen" is usually written as 女王 (Joō), Otohime was referred as 王妃 (Ōhi).