Also referred to as Carnunnos, Cernunnus, etc., his name translates as ‘The Horned One’ (Gaulish cernos, 'horn'). This name seems to be an epithet given in typical Gaulish fear that speaking the proper name of a deity might invoke the wrong kind of attention from him or her. Cernunnos is most-famously associated with the stag, ram, and ram-headed snake. He sometimes has a bag or bowl spilling grain or coins, or cornucopia and fruit.
He is recognized as the lord of animals, fertility, wealth, abundance, the regeneration of life, and the Underworld. He may have been, I think, the Dis Pater that Caesar referred to as the main god worshipped by the Gauls. A female half is also known, suggesting he had an complmentary Underworld and/or nature goddess as his consort. Some say she was the Celtic moon-goddess who, as with Diana and Artemis, etc., would also be a nature and animal goddess most closely identified with deer.
Parisii sailors dating from the reign of Tiberius depicted him as elderly, balding, and with the ears of a stag or human. A torc hung from each of his antlers. This unflattering depiction might have been reflected in Ireland as the Dagda. Elsewhere he is depicted with ram-horned or un-horned snakes, which is commonly interpretted as a phallic fertility symbol.
Some images have sockets for removable antlers. This could have been for seasonal removal or just to have authentic antlers on the image. His images are found widely in Gaul and Britain, though may have been a import into the latter area.
His most famous image is from the Gundestrap cauldron where he holds a serpent and torc, surrounded by a raven, dog, stage, and other animals in a scene strong with ritual but open to interpretation. That he is wearing an antlered cap and possibly an animal skin suit suggests the character is his priest. He sits in a yoga pose, recalling Hindu deities. Indeed, he may be linked to the Hindu stag-god Pashupati (pashu, 'animals', + pati, 'lord').
Cernunnos may be interpretted as a sacrificial god to whom sacrifices were made. By one scene of the Gundestrap cauldron, these sacrifices also included humans. These sacrifices were apparently made to maintain the balance and fecundity of nature and wild animals.
In addition to Pashupati, the horned god is found elsewhere in IE mythology as Karhuhas in Neo-Hittite mythology, Pan in Greece, and the Underwold gods Velns or Velinas in the Baltic, and with Veles or Volos in Slavic lands. The stag was also an important symbol to the various steppe peoples from the earliest IE tribes there to the Scythians and Sarmatians of late antiquity.
Elsewhere in Celtic myth, Cernunnos was reflected s Gwynn in Wales and especially Herne the Hunter in England. They both were was famous for their "Wild Hunt", riding out from their Underworld (or forest) abodes with their Hell Hounds in the winter hunting season. The sound of Herne, which in the Welsh story of Owain was the belling of a stag, was believed to portend an impending death. As a god of fertility, abundance, and regeneration, he could be, I think, reflected also in the Irish god Dagda, who had a rustic look, including animal-skin boots.
More certainly, I think we should identify Cernunnos with the Gaulish god referred to as Tarvos Trigaranos, 'Bull and Three Cranes'. Known chiefly from a monument found near Paris, as a horned animal the bull is his totemic animal. The three cranes, however, are not easily interpreted. However, they must represent the three aspects of Cernunnos as the god of life, death, and rebirth. Sometimes the Gallo-Romans depicted him with three heads or faces, also suggesting he was a triune god. This concept may have been the inspiration Triglav, the three-headed god of the Elbe Slavs who is unknown in eastern Slavic lands.
Elsewhere in Roman Europe, Cernunnos may have been the eponymous god of the Carnutes tribe in Gaul and the Cornavii in Britain. He also may have been named for the towns of Cenabum Carnutum, Canrona (mod. Chatelier), Cornille (Chambourg), Cornucio, and Cornutium. The first-metioned town, I think, may refer to Cernunnos' role as the 'Hound Lord', after the god Cunomaglus ('Hound Lord'), with the Cenomani tribes of Gaul and Transalpine Gaul and the Iceni tribe of Britain also naming themselves after this same god.
I believe the three cranes represent the three stages of life more commonly associated with the triple goddess but also part of Cernunnos' character of giving or regenerating life, providing wealth and abundance (maturity), and death.
Perhaps significantly, the Welsh goddess Rhiannon is also found with three birds. initially appeaing in Welsh myth outside an entrance to the Underworld. Indeed, her named is derived in part from Welsh annwn, 'Underworld'. Her name is also, I think, related to the Irish moon goddess Re or Ri, the Celtiberian goddess Rea and the Gallo-Roman goddess Rigatona. She may also be refected in the Greek goddess Rhea, wife of Cronos would likewise equated to Cernunnos, and the Baltic Underworld goddess Ragana, who may have been the wife of Velns.
Cernunnos is also known from various Celtic cardinal festivals that also record his cyclical nature. He was born at the winter solstice, marries the Goddess at Beltane (May Day, the beginning of summer), and dies at the summer solstice (as with the Norse's Balder). Finally, at Samhain he rides forth from the Underworld on his Wild Hunt.