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.[1]

Fidius may be an earlier form for filius, "son",[2] with the name Dius Fidius originally referring to Hercules as a son of Jupiter.[3] According to some writers,[4][5] the phrase medius fidius was equivalent to mehercule "My Hercules!", a common interjection.