|“||Did someone just call me the wine dude? It's Bacchus, please. Or Mr. Bacchus. Or Lord Bacchus. Or, sometimes, Oh-My-Gods-Please-Don't-Kill-Me, Lord Bacchus.||”|
–Bacchus on his name in The Mark of Athena.
Bacchus is Dionysus' Roman counterpart (split half). As Bacchus, he becomes more warlike, yet between Greek and Roman forms, he doesn't change much. Greek descendants see him as Dionysus.
Born to Jupiter and the mortal princess Semele, Bacchus was originally a demigod who was called upon by the gods (alongside his half-brother Hercules) to fight in the First Giant War as the Gigantes could only be killed by the combined efforts of a god and a demigod. He fought the Alodai twins, Ephialtes and Otis, and ultimately defeated them with the possible aid of the goddess Diana.
While not seen, Dakota is mentioned to be a child of Bacchus. Dakota has a hyperactive personality and addiction like his father, but instead of wine, he drinks red Kool-Aid with four times the normal amount of sugar.
Bacchus is waiting for Ceres in Topeka, Kansas at the mile marker 32. Bacchus talks to Percy Jackson, Jason Grace, and Piper McLean at the mile marker when they arrive. He does not recognize Percy as Bacchus. He relates that he fought in the first Giant War (as Dionysus) as a demigod. Whenever Percy mentions Dionysus he changes his form for a split second into his Greek form, Dionysus. He states that every time people think about him in his other form it gives him a headache, something that is also happening to all the other gods. Piper then asks him if he has a silver goblet and instead he pops a Diet Pepsi into his hand, which Percy finds strange due to the fact that as Dionysus he drinks Diet Coke. Piper states that he has to help them defeat the Giants. Irritated by her words, he tells her that he has to do nothing. He then quickly leaves after having realized that it was a trap set up by Gaea and that Ceres was not going to show up.
En route to Rome, Percy offers Chrysaor's ship, its millions of dollars worth of gold treasure, and a good deal of Diet Coke as a tribute to Bacchus, and it sinks into the Mediterranean Sea. Later, in Rome, Bacchus appears while Percy and Jason are fighting Ephialtes and Otis. He refuses to fight until he has seen a good show. After the two demigods continue to battle the giants in the Colosseum, Bacchus is sufficiently impressed by their abilities to join the fight and banishes both giants to Tartarus by tapping them with his Thyrsus rod. Bacchus tells Percy where to go to rescue Annabeth and makes comments that possibly indicate Percy and Annabeth's ordeal in Tartarus.
He is described as a youth of a plump figure, and naked, with a ruddy face, and an effeminate air; he is crowned with ivy and vine leaves, and bears in his hand a thyrsus, or javelin with an iron head, encircled with ivy and vine leaves: his chariot is sometimes drawn by lions, at others by tigers, leopards, or panthers; and surrounded by a band of Fauns, Bacchae, and Nymphs, in frantic postures; whilst Silenus, his preceptor, follows on an ass, which crouches with the weight of his burden.
- Bacchus' favorite drink (besides wine) is Diet Pepsi, much like how his Greek aspect's favorite drink is Diet Coke.
- Dionysus was originally named Bacchus by Zeus, on account of his screaming and yelling when he was born. As stated in Percy Jackson's Greek Gods, the name Bacchus means “the noisy one”.
- In antiquity the worshipers of Dionysus/Bacchus were collectively referred to as the Bakkhai.
- Bacchus' name, spelled in Latin as BACCHVS, is the Latinized form of the Greek name Βάκχος (Bákkhos), which was a primary epithet of Dionysus.