Vinegar Doppio is the Boss' younger, more innocent and eccentric underboss. As a member of Passione, he thinks of himself as the most loyal subordinate to Diavolo, but in reality, the two are separate souls inhabiting the same body. During the course of the Part, he helps Diavolo to act and move around undetected. It is ambiguous whether Doppio is truly a Stand User, but he is allowed to wield both King Crimson's arms and Epitaph in battle.

Doppio tends to be a friendly, honest, and bit cowardly. But he can be a violent and angry and times. His voice is in the high range.