Who is the Greek god of celebration?

I would assume it would be Dionysus, Greek God of Wine, Ecstasy, Civilization, Pleasure, etc, and threw wild parties. He basically is the symbol of a large celebration and was widely loved and worshiped, especially at parties or where there was wine drinking.

There is no other God, really, who stayed amongst mortals/loved them as much as Dionysus. Maybe Zeus, but none of the other Gods cared about mortals that much, let alone go to a party with them.

Hope this helps in any way! :)