Can a religion have no creator god?

Yes. Scholars call them nontheistic religions, and they are not the same as atheism: they have rituals, ethics, monks, temples and a sense of the sacred, but they do not rest on a creator god. Nontheism plays a major role in Jainism, Buddhism and parts of Hinduism, and traditional Taoism and Confucianism are often counted too.

Jainism is the clearest case. In Jain teaching, the universe, its matter and its souls are eternal and uncreated: there is no omnipotent creator. Heavenly beings exist, but they are mortal and do not create anything. The beings Jains revere, the Tirthankaras, are souls who freed themselves from karma; they are "gods" only in that sense. One Jain teacher, Jinasena, mocked the alternative: some foolish men declare that a creator made the world, he wrote, but where was this God before creation, and what raw material did he use?

Buddhism also denies a creator deity, and has done so since the Buddha's time. The Buddha said gods exist, but described them as trapped in the cycle of rebirth like everyone else. When a monk pressed him on unanswerable metaphysical questions, he told a parable: a man shot with a poisoned arrow refuses treatment until he learns who shot it and why, and dies before he finds out.

These examples matter for the very definition of religion. Many definitions assume a god; these traditions show that religious practice and belief can do without one.