Aramaki, better known by his alias Ryokugyu, is an admiral in the Marines. He attained his rank during the two-year timeskip, along with Fujitora, both filling the two admiral vacancies left by Aokiji and Akainu.

He was first mentioned by Donquixote Doflamingo in the Dressrosa Arc, and debuted in the Reverie Arc. His full appearance and real name were revealed near the end of the Wano Country Arc.

(Source: One Piece Wiki)