Kansa, the ruler of Mathura, was a greedy and ruthless man. He was a tyrant and the people of Mathura were terrified of him.
Kansa loved his sister, Devaki, dearly. When Devaki was getting married, Kansa decided to be the charioteer of the bridal chariot and drive Devaki and her husband, Vasudeva, through his kingdom.
While driving the chariot, Kansa heard a voice from the heavens above, "You fool, your days on earth are nearing their end!
Kansa was startled. The voice roared again, "The eighth child of Devaki will kill you." Kansa wanted to kill his sister but Vasudeva begged Kansa to spare them and promised to surrender all his children to Kansa.
Kansa agreed but immediately threw them in prison. He killed the first six children as soon as they were born but Krishna and Balarama were saved by Vasudeva's quick thinking. Years later the prophecy proved true and Krishna killed Kansa.