Sengoku the Buddha: Sengoku is a former Fleet Admiral of the Marines and one of the most powerful members of the organization. He is one of the few Marines known to possess Conqueror's Haki, and has demonstrated this ability on multiple occasions.
Sakazuki (Akainu): Sakazuki is the current Fleet Admiral of the Marines and one of the strongest characters in the series. While he has not been shown to use Conqueror's Haki in the series, it has been confirmed in a databook that he possesses this ability.
Kizaru (Borsalino): Kizaru is an Admiral in the Marines and one of the strongest characters in the series. While he has not been shown to use Conqueror's Haki in the series, it has been confirmed in a databook that he possesses this ability.
Issho (Fujitora): Issho is an Admiral in the Marines who was introduced in the Dressrosa arc. He has not been shown to use Conqueror's Haki in the series, but it has been stated in a databook that he possesses this ability.
Tsuru: Tsuru is a Marine Vice Admiral and one of the highest-ranking female members of the organization. While she has not been shown to use Conqueror's Haki in the series, it has been confirmed in a databook that she possesses this ability.
+ Garp