Dis Pater, or Dispater, was a Roman and Celtic god of the underworld, later subsumed by Pluto or Jupiter. Originally a chthonic god of riches, fertile agricultural land, and underground mineral wealth, he was later commonly equated with the Roman deities Pluto and Orcus, becoming an underworld deity.Dis Pater was commonly shortened to simply Dis. This name has since become an alternate name for the underworld or a part of the underworld, such as the Dis of The Divine Comedy.
Etymology
Dis Pater was originally a god of wealth, much like the Greek god Pluto (from Greek ???????, Plout?n, meaning "wealthy"), who was later equated with Dis Pater. Dis is contracted from the Latin dives ("rich"), and pater is Latin for "father", the literal meaning of Dis Pater being "Wealthy Father" or "Father of Riches".Julius Caesar writes in Commentarii de Bello Gallico that the Gauls considered Dis Pater to be an ancestor. This may in part be due to confusion between Dis Pater and the Proto-Indo-Europe
Source:
http://en.wikipedia.org/wiki/Dispater