Vasudeva

Once upon a time, Vasudeva, the son of Surasena, just after marrying Devaki, was going home on his chariot with his newly wedded wife. At that time, Kamsa, the son of Ugrasena, in order to please his sister, Devaki, had voluntarily taken the reins of the horses of Vasudeva's chariot and was driving. While the bride and bridegroom were passing along on the chariot, suddenly there was a miraculous sound vibrated from the sky which announced that the eighth child of Devaki will kill Kamsa. Immediately Kamsa caught hold of Devaki’s hair and was just about to kill her with his sword. But Vasudeva intervened promised that he will present all the children born of Devaki to Kamsa. 

When the first child was born, Vasudeva immediately brought the child before Kamsa. Kamsa returned the child to Vasudeva because according to the prophecy the danger was from the eighth child. But when he learnt from Narada that all the demigods are born in the family of Vrshnis, he became alarmed. He arrested Vasudeva and Devaki and put them behind prison bars. He also decided to kill all the babies who took birth from Devaki and Vasudeva. Thus he killed the first six babies. Lord Balarama appeared as the seventh son in the womb of Devaki. 

At this time, Krishna, the Supreme Lord, ordered the appearance of Yogamaya, His internal potency. Yogamaya is the principal potency of the Personality of Godhead. The Supreme Lord ordered her to transfer Lord Balarama from the womb of Devaki to the womb of Rohini. Rohini was one of the wives of Vasudeva and she was residing at the house of Nanda Maharaja and Yashoda in Vrindavana. As ordered by the Supreme Lord, Yogamaya transferred Lord Balarama from the womb of Devaki to the womb of Rohini. On account of being forcibly attracted to the womb of Rohini, He is also known as Sankarshana. 

Thus ordered by the Supreme Personality of Godhead, Yogamaya circumambulated the Lord and then appeared within this material world according to His order. When Yogamaya, the supreme power of the supremely powerful Personality of Godhead, transferred Lord Sesa from the womb of Devaki to the womb of Rohini, both Devaki and Rohini were under Yogamaya's spell, which is called yoga-nidra. When this was done, people thought that Devaki's seventh pregnancy had been a miscarriage. Thus although Balarama appeared as the son of Devaki, He was transferred to the womb of Rohini to appear as her son.