Bacchus

"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. As Bacchus, he becomes more warlike. Yet between Greek and Roman forms he doesn't change much.

History
Bacchus is the god of wine and intoxication. Though he represents raving lunacy and uncontrollable passion, he also represents personal liberation and unity with nature.

He was the god of good-cheer, wine, and hilarity; and of him, as such, the poets have not been sparing in their praises: on all occasions of mirth and jollity, they constantly invoked his presence, and as constantly thanked him for the blessings he bestowed. To him they ascribed the forgetfulness of cares, and the delights of social converse.

The women who accompanied him as his priestesses, were called Maenades, from their madness; Thyădes, from their impetuosity; Bacchae, from their intemperate depravity; and Mimallones, or Mimallonides, from their mimicking their leaders.

The victims agreeable to him were the goat and the swine; because these animals are destructive to the vine. Among the Egyptians they sacrificed a swine to him before their doors; and the dragon, and the pyre on account of its chattering: the trees and plants used in his garlands were the fir, the oak, ivy, the fig, and vine; as also the daffodil, or narcissus. Bacchus had many temples erected to him by the Greeks and the Romans.

The Son of Neptune
While not seen, Dakota is mentioned to be a child of Bacchus. Dakota has a slightly addictive personality like his father, but instead of wine, he drinks red Kool-Aid with four times the normal amount of sugar.

The Mark of Athena
Bacchus is waiting for Ceres in Topeka, Kansas at the mile marker 32. Bacchus talks to Percy, Jason, and Piper 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. Piper then asks him if he has a silver goblet and instead he pops a Diet Coke into his hand. Piper states that he has to help them defeat the Giants. He tells her that he has to do nothing. He then 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. Later, in Rome, Bacchus appears while Percy and Jason are fighting Ephialtes and Otis. 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.

Representation
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.

Trivia

 * Bacchus' favorite drink (besides wine) is Diet Pepsi, much like how his Greek aspect's favorite drink is Diet Coke.
 * As of The Mark of Athena, Bacchus is currently the only god to fight against his Gigantes counterparts.