Dius Fidius

In ancient Roman religion, Dius Fidius (less often as Dius Fidus) was a god of oaths associated with Jupiter. His name was thought to be related to Fides.

Fidius may be an earlier form for filius, "son", with the name Dius Fidius originally referring to Hercules as a son of Jupiter. According to some writers, the phrase medius fidius was equivalent to mehercule "My Hercules!", a common interjection.