In Terry Pratchett’s fantasy novel Small Gods, the Great God worshipped in Omnia is Om.
Om is the central deity of the Omnian religion, a powerful theocracy whose priests claim authority in his name. The novel’s viewpoint character, Brutha, is an unusually devout novice who encounters Om in the form of a one-eyed tortoise. Their relationship exposes the difference between genuine belief and institutional religious power.
Pratchett’s satire distinguishes the god himself from the large bureaucracy built around him. Om’s strength depends on believers, but the Omnian Church has become more concerned with doctrine, punishment, and political control than with the values it claims to represent.
Om should not be confused with other Discworld gods. Blind Io is associated with the traditional pantheon of many gods, Anoia is the goddess of things that get stuck in drawers, and Offler is the crocodile-headed god. Om is specifically the deity of Omnia in Small Gods.