Subhadra is the sister of Krishna. She is considered an incarnation of Maya who appears as per the instructions of Krishna. Subhadra was married to her first cousin Arjuna, the Pandava, who was the third son of Kunti.
Subhadra and Arjuna were the parents of Abhimanyu, whose posthumous son Parikshita, born to the widowed Uttara, was the sole surviving dynasty of the entire Kuru family.
The epic Mahabharata is a story based on the Kuru family as well as the Pandavas. Subhadra is an important character in that epic.