Aramaki

Ryokugyu is an admiral of the Marines. He was briefly mentioned by Doflamingo.

Abilities and Powers
Not much is known about his abilities, but as a Marine Admiral, Ryokugyu must have at least above-average leadership and co-ordination skills, and has power over thousands of lower ranked Marines. As an Admiral, Ryokugyu has the authority to enact a Buster Call on any island he deems dangerous, and may pass this abiltiy to a lower ranking World Government agent.

Haki
It was stated that all Marines ranked vice admiral or higher possess Haki, so as a higher ranked officer as well as leader of the Marines, Ryokugyu can also use the ability.

Past
Not much is known about his past, but sometime during the two years the Straw Hats were separated, he was promoted to admiral.

Dressrosa Arc
He was briefly mentioned by Doflamingo whilst talking to Fujitora, calling him and Fujitora "Beasts" in terms of power.