About Five Elders
The Five Elders are a council of the five highest-ranking Celestial Dragons collectively titled the "Highest Authorities of the World Government" (世界政府最高権力, Sekai Seifu Saikō Kenryoku?). Publicly claimed to oversee and wield the greatest authority over the entire world at large, they are secretly subordinate to the government's shadow ruler Nerona Imu, the true King of the World and occupant of the Empty Throne. They are almost always found residing in the Room of Authority in Pangaea Castle.
The Five Elders (in particular Jaygarcia Saturn) are the main antagonists of the Egghead Arc. Due to their status, longstanding actions both indirect and direct, and their profound plot involvement, they can be considered among the main antagonists of the Final Saga as well as the One Piece series as a whole.
As their name indicates, the Five Elders consist of five different members of the World Nobles. The original Five Elders, introduced at the beginning of the series during the Jaya Arc, consisted of Jaygarcia Saturn, Marcus Mars, Topman Warcury, Ethanbaron V. Nusjuro and Shepherd Ju Peter. It is known that at least Jaygarcia Saturn has been in service of the group for centuries, as he was present during Emet's attack on Mary Geoise roughly 200 years ago.
Imu appears to have the authority to appoint a new Elder as replacement for an older one, with the role, duties, and title of the latter being passed down to the former as a result. The only known case of this happening so far has been Saturn being succeeded by Figarland Garling following the events of the Egghead Incident.