Devaki was a woman mentioned in the Mahabharata. Her father’s name was Devaka, and she was the younger sister of Kansha, a cruel king of Mathura of Ancient India. Devaki was married to Vasudeva, a son of Sureshana. Krishna, an avatar of Vishnu (a god of Hindus) was son of Devaki and Vasudeva.She was Krishna's real mother.
She had 8 sons in total including Krishna. The first six of her children were killed by her brother Kamsa. The seventh time there was a miscarriage and Balaram got carried to Mother Rohini's womb. All the time she was in prison by Kamsa till he released them out of pity. You can find more at the book Krsna by His divine Grace A.C Bhaktivedanta Swami Srila Prabhupada.