Proto-Germanic *Rīnaz, from Gaulish Rēnos, from a Pre-Celtic or Proto-Celtic *Reinos; one of a class of river names built from Proto-Indo-European *h₃reyh₂– (“to move, flow, run”). Cognate with Old High German Rīn (“the Rhine”; > German Rhein), Old Norse Rín (“the Rhine”), Dutch Rijn (“the Rhine”)
Among the Romans he was known as Rhenus Pater (Father Rhine) or Rhenus Bicornis (Two-Horned Rhine). Throughout the Rhine land, such as areas near Cologne, various statuary and votive stones from the 3rd century have been found which depict his iconography and/or dedications to his name. One such find reads:
RHENO PATRI OPPIVS SEVERVS LEG AVG
“Oppius Severus, representative of Augustus, made this for Father Rhine”
In his depictions he is often shown as an old man with flowing hair, mouth agape. In those images where he is shown with his head adorned with two horns, he at times appears with a jar tipped over and water flowing therefrom.
According to Propertius, the 3rd century Gaulish warlord named Virdomarus, who was killed at the hands of Consul Claudius Marcellus, claimed he was descendant from the god of the Rhine:
Claudius also threw the enemy back when they’d crossed the Rhine, at that time when the Belgic shield of the giant chieftain Virdomarus was brought here. He boasted that he was born of the Rhine itself, agile at throwing a Gallic javelin from the unswerving chariot wheels.
Votive stones have shown him depicted along various deities such as Jupiter, Juno, Minerva, Neptune and Oceanus, as well as other generic Genius Loci.
The Gallic or Belgic warlord, Virdomarus, may have been Germanic or at the very least culturally Germanic, his name being *Wirdomar meaning “famed lord”:
From Old Dutch *wird “lord, host protector”, Middle Dutch waert. Cognate with German Wirt “innkeeper”. (See Wirdskapon for more on Wird)
This correlation with a “famed lord” may put him in relation to Merovech who shares a similar name “famed warrior” who, according to Fredegar, was also descendant from a horned river god (Bistae Neptuni quinotauri similis).
As the depictions of Rhenus Pater, or in TFA Rîn Fader, are found all throughout the Rhine delta, he may be viewed as a god who rules over all rivers. In the area of Xanten, coins, statuary and weapons have been found over a number of centuries indicating that cultus was offered to the river. In all regions where the Franks were to be found, there were offerings to the rivers.
Ahuardua, the “Water, Sublime Goddess” can be seen as a relative counterpart or consort of Rîn Fader, whereas he is related to the rivers and fast flowing water ways (maybe even springs), she is viewed, in TFA, as holding sway over the flooding tides and deeper waters of lakes and oceans.