The principal subject of the The Bacchae, Dionysus, possesses a multitude of powers and can take a variety of forms. In Euripides's conception of the god, however, his numerous forms conform to the logic of duality, that is, they are both one thing and its opposite simultaneously. Thus, Dionysus is presented as being both inside and outside the play's action. Physically, he is both beautiful and fearful. By birth, he is both divine and human, the son of Zeus and a mortal woman. By origin, he is both Greek and Asiatic, his cult associated with Asia Minor. His cult names provide insight into the nature of his relationship with humankind: the bacchants call him Bromios, "the roaring one", and also Lysios, "the god of letting go". Dionysus's gifts allow humans to let go of their troubles through wine, to let go of their identities through theater, and to let go of their individuality through cult worship. For humans, his ability to allow them to let go, when practiced in moderation, opens them to the festive, communal side of life. As the Stranger, or Dionysus's human form, says, "Dionysus, as a god in perfect essence: a terrible one, but to men most gentle."

But this letting go, like everything associated with Dionysus, also has its potential dark aspect. There is no inherent limit to the powers of bellowing Dionysus. Festivity can turn to destructive excess, and instead of providing a necessary temporary release, can overpower life itself. Without self-control, Dionysus's powers can drive humans to let go of their sanity, to let go of their judgment and, in the end, to let go of their very humanity. The supreme importance of self-control is embodied by none other than the disguised Dionysus. While Euripides vividly illustrates the full extent of Dionysus's ecstatic powers upon his followers, the Stranger himself is calm, self-possessed and patient. He alone displays self-control and wisdom, and these traits distinguish him from the mortals who surround him. While he is able to sting men with madness, he is the picture of sanity, suggesting that he is not the agent of the tragedy, but perhaps that mortals themselves are responsible for their bloody discord.