Short answers, pulled from the story.
Dionysus is the ancient Greek god of wine-making, orchards, fruit, vegetation, fertility, festivity, insanity, ritual madness, religious ecstasy, and theatre. He was also known as Bacchus, a name the Romans later adopted, referring to the frenzy called baccheia that he was said to induce.
The earliest written records of Dionysus worship come from Mycenaean Greece, specifically around the Palace of Nestor in Pylos, dated to around 1300 BC. His name appears in Linear B tablets as di-wo-nu-su-jo, linking him to offerings or payments of wine.
Major festivals dedicated to Dionysus included the Rural Dionysia, held in winter, the City Dionysia near the spring equinox, and the three-day Anthesteria celebrating the beginning of spring. The dramatic competitions at the City Dionysia were the initial driving force behind the development of theatre in Western culture.
The Roman Senate issued the Senatus consultum de Bacchanalibus in 186 BC, banning the Bacchic cult organisations after the state treated them as a subversive counter-culture. Of roughly seven thousand people arrested, most were executed. The edict limited meetings to no more than three women and two men and required prior senatorial approval through a praetor.
Dionysus was described as being born multiple times. In the Orphic tradition he was first born to Zeus and Persephone, then dismembered by the Titans and reborn. His second birth came from Zeus and the mortal Semele; after Semele was killed by a thunderbolt, Zeus sewed the infant into his thigh until birth, earning Dionysus the epithet Dimetor, meaning twice-born.
Dionysus was identified with multiple deities across cultures. As early as the fifth century BC, Greeks had syncretised him with the Egyptian god Osiris into a deity known as Dionysus-Osiris. The philosopher Heraclitus argued that Hades and Dionysus were the same god. Some ancient writers also recorded a widespread belief that Yahweh was identifiable as Dionysus through the Phrygian god Sabazios.