Gopa or Gop or Gope is a synonym of the Ahir (Yadav) caste found in India and Nepal. in the Mahabharata, Ahir, Gopa, Gopal and Yadavas are all synonyms. The Amarakośa mentions Gopa, Gopāla, Gosaṁkhya, Godhuk and Ballava as the synonyms for Abhira and says that the village or place where Abhiras lived is named as Ghosha or Abhirapalli. The modern Ahirs are the descendants of the Abhiras of ancient times. The Abhiras were the same as the Gopas or Ballavas of Mathura becomes evident from the fact that the Padma Purana relates that Vishnu informed the Abhiras: I shall be born amongst you, O Abhiras, at Mathura in my eighth birth.
The Yadavas of the Mahabharata period were known to be the followers of Vaishnavism, of which Krishna was the leader: they were Gopas (cowherd) by profession, but at the same time they held the status of the Kshatriyas, participating in the battle of Kurukshetra. The present Ahirs/Yadavs are also followers of Vaisnavism.
In Harivamsa Purana, it has been said that Gopas and Yadav are generic of same lineage and they are called Gop or Yadav.
Origin and History
According to Bhagavata Purana, The Gopas are re-incarnation of Devas. They are the messengers of Krishna, They are fond of Gavya or the products of Cows. The relation between Krishna and the Gopas is that between an object and its image.
In Rigveda, King Yadu (ancestor of the Yadavas) is mentioned as Gopa, here the term Gopa may have been used to refer to the king or chief of the tribe as Gopa or Gopati was also the epithet given to the king in that period.
Mahabharat's Narayani (Gopayan) Army
Narayani Sena (Gopayan) or Yadav(Ahir) Sena, the army of Lord Krishna of Dwarka Kingdom is called as the supreme sena of all time. It is described in the Mahabharat as being all of the Abhira caste. They were the basic threat to the rival kingdoms. Fearing Narayani Sena, many kings do not tried fighting against Dwarka. Because Dwarka sorted most of the threats through Krishna's politics and talent of Yadavas. Using Narayani Sena, the Yadavas extended their empire to most of India.
Krishna had offered Arjuna, the choice of selection between him or his whole army of Narayani Sena against Duryodhana. He possessed 10 million fighting Gopas who were brave fighters and were famous by the name of Narayan. In Harivansa Purana, it has been said that Gopa or Yadav are generic of the same lineage.
Before the war started in the Kurukshetra battlefield in Mahabharat (one of the two major epics of ancient India), both sides – the Kauravas and the Pandavas started out in all directions to meet various kings to solicit support. Incidentally, both Duryodhana (from Kauravas side) and Arjuna (from Pandavas side) reached Dwarika, the kingdom of Shree Krishna together. Lord Krishna put forward a condition in front of both – you can have either me on your side or my entire army, the Yadav army – known as the Narayani Sena. He also told both that he wouldn't take to any arms during the entire war. So when Krishna first asked Arjun what he wanted, much to Duryodhana's delight, he opted for the Lord- 'Narayan' and Duryodhana got these great warriors of the strong army-the Narayani Sena. When Narayani Sena was fighting for Kauravas, only Kritavarma and his army unit fought for the Kauravas. Satyaki fought for the Pandavas. The rest of the Atirathas and Maharathis were withheld from the Kurukshetra war on the advice of Balram and Krishna.
These Gopas, whom Krishna had offered to Duryodhana to fight in his support when he himself joined Arjuna's side, were no other than the Yadavas themselves, who were also the Abhiras. They were the supporters of the Duryodhana and Kauravas, and in the Mahabharata, Abhir, Gopa, Gopal and Yadavas are all synonyms. They defeated the hero of Mahabharatha war (Arjuna), and spared him when he disclosed the identity of the members of the family of Sri Krishna.