The Communications Satellite Ark (通信衛星アーク, Tsūshin Eisei Āku), also simply known as the Ark (アーク, Āku), is the main antagonist of Kamen Rider Zero-One. It is an artificial intelligence that transforms into Kamen Rider Ark-Zero (仮面ライダーアークゼロ, Kamen Raidā Āku Zero).