Dionysus

Dionysus is the greek god of wine, revels, ecstatic violence, and madness. He is mentioned in "Last Call" and Skin Game.

"Last Call"
In "Last Call", Meditrina Bassarid states that it is the time for mortals to be reminded of his power.

Skin Game
In Skin Game, it is implied that all the Olympian gods exist in some form, as Hades tells stories of his life confirming their existence.