Dionysus was the only one of the Olympian gods to have a mortal mother. Dionysus' Roman name was Bacchus. He was the god of wine and often threw crazy parties.
Dionysus plays a very minor role in the film usually only appearing in cameos.
During the beginning of the film, he is present for the party celebrating Zeus and Hera's newborn son, Hercules. Eighteen years later, Hades unleashes the Titans on Mount Olympus and imprisons all the Gods including Dionysus. Luckily, they are all saved by Hercules. Near the end of the film, he is seen celebrating Hercules' arrival after having gained his Godhood, but when Hercules decides to live as a mortal on Earth with Megara, Dionysus still celebrates Hercules' decision, even opening a bottle of wine in celebration of the new couple