Poseidon (ポセイドン) is the main antagonist of Kamen Rider OOO: Ankh's Resurrection, The Medal of the Future and The Leading of Hope. He was a Greeed from the future who possessed Michal Minato and became Kamen Rider Poseidon (仮面ライダーポセイドン, Kamen Raidā Poseidon).