Did the Ancient Greek Philosophers actually believe in their Gods and Myths?

When did Greece stop believing in gods?

9th century CE

The majority of modern historians agree that the religion practiced by the ancient Greeks had been extinguished by the 9th century CE at the latest and that there is little to no evidence that it survived (in public form at least) past the Middle Ages.

Who was the ugliest god?

Hephaestus

Hephaestus. Hephaestus is the son of Zeus and Hera. Sometimes it is said that Hera alone produced him and that he has no father. He is the only god to be physically ugly.