Balarāma was the elder brother of Kṛṣṇa. He was conceived as the seventh son of Devakī by Vasudeva. But the foetus was drawn out of her by Yogamāyā (divine power) and placed in the womb of Rohiṇī, the elder wife of Vasudeva, living at Nandagokula. So he was born as the son of Rohiṇī. Since he was extraordinarily strong, he was called ‘Balarāma’ (bala = strength). He had several other names like Saṅkarṣaṇa, Rauhiṇeya, Musalī, Halī, Nīlāmbara and so on. As per the paurāṇic lore, he was the incarnation of Ādiśeṣa (the serpent on which Viṣṇu is resting in the Kṣīrasāgara or ocean of milk) come down to help Kṛṣṇa who was Viṣṇu himself. He was an expert in fighting with gadā or mace. The plough (halā) was his favourite weapon. The Bhāgavata is full of his exploits. Along with Kṛṣṇa, he too killed many a demon like Pralamba, Dhenuka, Dvivida and Balvala. After the killing of Kaṁsa by Kṛṣṇa, Balarāma too got his formal education under the sage Sāndīpani. He married Revatī, the daughter of the king Revata. When the Kauravas of Hastināpura had abducted Sāmba, a son of Kṛṣṇa, he went there and rescued him. It was he who taught gadā-vidyā (the science of fighting with the mace) to Bhīma (the second of the five Pāṇḍavas) and Duryodhana (the eldest of the Kauravas). He had a soft corner for the latter.
During the Kurukṣetra (or Mahā-bhārata) war, he refused to participate but went away on a pilgrimage. He reappeared at the time of the duel between Bhīma and Duryodhana. He tried to prevent it but did not succeed. He was cross with Bhīma for having flouted the rules of mace-fighting but was pacified by Kṛṣṇa.
When the Yādavas exterminated one another in mutual fighting, Balarāma sat in yoga and left the body in the form of a serpent thus confirming that he was Ādiśeṣa.
See also KṚṢṆA.