Dr. Hebereke

Dr. Hebereke is the true leader of the Roborobo Gang (known as the Rubberobo Gang in the dub), whose ultimate goal is to obtain Rare Medals in order to conquer the world. He first appears as a disembodied presence on a television screen within the gang's headquarters. In his early appearances, his face remains hidden, with only his cat visible.

When one of the four Rubberobo leaders acquires a Medal, they summon Dr. Hebereke, who manifests as a swirling spiral cloud in the sky.

(Source: Medarot Wikia, edited)