Kunti was the daughter of Shurasena, a Yadava ruler of Mathura but, was raised by her childless uncle Kuntibhoja, the King of Kuntibhoja. She was the sister of Krishna’s father, Vasudeva.
Once Sage Durvasa visited Kuntibhoja, and pleased by Kunti’s devotion, he taught her a mantra, through which she could beget a child from any God she desires.
Kunti was curious and recited this mantra, invoking Surya deva. Later, she gave birth to a boy, named Karna.
Kunti was not married yet, so she begged Surya deva to take the child back but he refused, but blessed Karna, with a divine armor and earrings. She put Karna in a basket and left him in River Ganga.
Years later, when Kunti’s Swayamvara was organised, she chose Pandu, the King of Hastinapur, to be her husband. Soon after their marriage, Pandu went on to expand his kingdom, Bhisma proposed that Pandu should marry Madri, the princess of Madra Kingdom, in order to secure the kingdom of Madra.