Dionysus (Bacchus) was the Greek god of revelry and pleasure. Depending on which painted vase you’re looking at, he was either an old man with a beard, or a pretty boy with long hair. He was the son of Zeus and a princess of Thebes named Semele (or possibly he was a son of Zeus and Demeter, Io, Dione, Arge, Persephone, Io, or Lethe, or possibly the son of Ammon and Amaltheia, but let’s go with Semele). While Semele was pregnant with Dionysus, Zeus promised her anything she asked. Hera tricked Semele into asking to see Zeus in his full glory. Zeus, bound by his promise, had to comply, and Semele burned to a crisp. Zeus managed to save Dionysus by sewing him into his thigh and carrying him to term. (The gods are SO weird!)
OR Dionysus is a son of Demeter or Persephone and Zeus and was sent to be eaten by the Titans by a jealous Hera. Zeus swooped in to save the day and found they’d already eaten everything but his heart. Athena or Rhea or Demeter managed to restore him from that by placing the heart in Zeus’s thigh until he reformed and Zeus gave birth. Because of this dying then being born thing, he’s considered a death and rebirth deity.
After giving birth, Zeus sent Dionysus to live (in some versions of the myth disguised as a girl) with Semele’s sister, Ino, and brother-in-law, Athamas (He may have lived with some nymphs prior to moving in with his aunt and uncle, or he might have lived with a daughter of Aristaeus, and Athena named Nysa, or Hermes, or Persephone, or Rhea). Hera, enraged to discover the child still lived, drove Ino and Athamas insane. They killed their children and then themselves. In some versions of the myth, Zeus saved Athamas from madness by turning him into a ram and having him take the young Dionysus into a cave on Mount Nysa, where he was then brought up by Nymphs. I’m sure Athamas appreciated being rescued from madness after his wife and children were slaughtered by his own hands.
Dionysus grew up among one group of nymphs or another (his origin stories are vast if you can’t tell. There’s about as many different versions as there were people in ancient Greece), and possibly took lessons from Chiron. As an adult, Hera cursed him with madness and forced him to roam the country side introducing people to the wonders of wine. This trick had a profound impact on the young Dionysus, and violence and madness became his go-to punishment. King Lycurgus angered Dionysus and ended up killing his entire family and then himself with an ax (he thought they were vines). King Pentheus was torn limb from limb by his daughters and/or wife, King Proteus was flayed alive for refusing the introduction of the grape vine, a group of pirates leapt overboard convinced they were dolphins, women who didn’t acknowledge his divinity ate their young, a nymph who pursued him was (predictably) turned into a plant, and so on. This was not a guy you wanted to upset. Despite that bloody history, he was regarded as a god of peace, civilization, and law.
He was also all about partying. His bacchanalias were famous. He went everywhere, establishing towns, introducing wine, driving out and killing invading amazons. He cursed Midas with the golden touch (though it was intended to be a gift) and eventually journeyed to the Underworld and led his mother back to the realm of the living.
In some versions of the myths he could tell the future or heal mankind. He was often seen as a god of art or protector of theater.
Dionysus came about fairly late in the Pantheon, and some interpretations of the myth suggest many myths involving Demeter may have been altered to give Dionysus credit (I mean, think about it, she was the goddess of the harvest, wine should be her thing). He’s also virtually identical to Iachus and a few more minor mythological gods and figures that may have combined to create one deity. Other interpretations consider him to be another aspect of Hades because “the cult of Dionysus is also a “cult of the souls”; his maenads feed the dead through blood-offerings, and he acts as a divine communicant between the living and the dead” (thank you wikipedia).
You’ll notice Dionysus isn’t included in my books, like, at all. That’s mostly because he is such a compilation of other deities that I have included/may include in my books. His insanity is reflected in Zeus, his chthonic tendencies in Hades, his powers in Demeter. Orpheus and some not-yet-introduced characters share other characteristics. Plus, he’s technically a demigod, so if he did exist in my universe, his time would have already come and gone.